Wireless communication system, wireless communication apparatus, wireless communication method and computer program

ABSTRACT

The present invention eliminates a transmission-waiting operation which is unnecessary while accommodating a prioritized traffic. Although a communication station enters a transmission-disallowed state in response to detection of a signal addressed to another station in accordance with medium access control based on CSMA, if the communication station receives a frame transmitted with priority to a local station during the transmission waiting, it cancels the transmission-disallowed state, sends back a frame responding the frame transmitted with priority and effectively operates a transmission prioritized period. The communication station starts a search procedure to perform a processing of evading duplication of the transmission prioritized periods if it judges a possibility of a problem occurring in a time zone in which reception with priority is possible.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese PatentApplications JP 2004-56776 and JP 2005-048878 filed in the JapanesePatent Office on Mar. 1, 2004 and Feb. 24, 2005, respectively, theentire contents of which being incorporated herein by reference.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

The present invention relates to a wireless communication system formutual communication among a plurality of wireless stations such as awireless LAN (Local Area Network), a wireless communication apparatus, awireless communication method and a computer program, and moreparticularly to a wireless communication system, a wirelesscommunication apparatus, a wireless communication method and a computerprogram, in which a wireless network is configured by each stationoperating in a self-organized distributed manner.

To be more precise, the present invention relates to a wirelesscommunication system, a wireless communication apparatus, a wirelesscommunication method and a computer program, all enabling eachcommunication station to perform medium access control in accordancewith the Carrier Sense Multiple Access (CSMA) system or the TimeDivision Multiple Access (TDMA) system in an autonomous distributed typewireless communication environment. In particular, the present inventionrelates to a wireless communication system, a wireless communicationapparatus, a wireless communication method and a computer program, allenabling each communication station to evade mutual interference whileperforming communication securing a band by providing a prioritizedutilization region.

As one of the standard specifications of wireless networks, IEEE (TheInstitute of Electrical and Electronics Engineers) 802.11 (e.g., referto Non-patent Document 1), HiperLAN/2 (e.g., refer to Non-patentDocument 2 or Non-patent Document 3), IEEE 802.15.3, Bluetoothcommunication and the like can be enumerated. The IEEE 802.11 standardincludes extended standards such as the IEEE 802.11a (e.g., refer toNon-patent Document 4), b, g and the like, depending upon a differenceof a wireless communication scheme and a frequency band in use.

In general, in order to configure a local area network by using wirelesstechnologies, a method is used by which one apparatus to be used as acontrol station called an “access point” or a “coordinator” is installedin an area and a network is formed under the collective control by thecontrol station.

In a wireless network disposing access points, in a case whereinformation is transmitted from a certain communication apparatus, anaccess control method based on bandwidth reservation has been adoptedwidely by which a band necessary for transmitting the information isfirst reserved at an access point to use a transmission path withoutcollision of information transmission with other communicationapparatuses. Namely, synchronous wireless communication is performed bymutually synchronizing with communication apparatuses in the wirelessnetwork by distributing access points.

In a case where asynchronous communication is to be performed betweencommunication apparatuses on the transmission side and reception side ina wireless communication system having access points, this wirelesscommunication requires by all means wireless communication via an accesspoint so that there arises the problem that a transmission path useefficiency is decreased by half.

As another method of configuring a wireless network, “Ad-hoccommunication” has been devised in which terminals perform wirelesscommunication directly and asynchronously. It can be considered that thead hoc communication in which arbitrary terminals perform wirelesscommunication directly without using a particular access point issuitable particularly for a small scale wireless network configured witha relatively small number of clients positioned near each other.

The Ad-hoc wireless communication system has no central controllingstation so that it is suitable for configuring a home network whichcomprises home electric appliances. The ad-hoc network is characterizedin that: the routing is automatically changed if one terminal is inerror or turned off so that the network is not easily broke down; and aplurality times of hopping of a packet between mobile stations makes itpossible to transfer data relatively further while keeping high datatransfer rate. Various developing examples of the ad-hoc system havebeen known (e.g., refer to Non-patent Document 5).

For example, in a wireless LAN system of IEEE802.11 system, thenetworking in the IEEE 802.11 is based on the concept of a basic serviceset (BSS). The BSS is composed of two kinds of modes, namely BSS definedby an infrastructure mode, in which a master such as an access point(AP) functioning as a controlling station exists, and an ad hoc modecomposed of only a plurality of mobile terminals (MTs) functioning asmobile stations. The ad-hoc mode, the latter, operates peer to peer in aself-organized manner without having a relation of a controlling stationand a controlled station. In this operation mode, when a beacontransmission time comes, each terminal starts counting a random timeperiod and in a case where it receives no beacon from another terminalby the end of the time period, it transmits a beacon.

Now, IEEE 802.11 is exemplified to describe the details of theconventional wireless networking.

<Infrastructure Mode>

In the BSS at the time of the infrastructure mode, an access pointperforming coordination is indispensable in a wireless communicationsystem. In other words, the access point arranges a range in which radiowaves can reach around a local station as BSS, and configures a “cell”so referred to in a so-called cellular system. A mobile terminalexisting in the neighbor of the access point is accommodated in theaccess point to enter the network as a member of the BSS.

The access point transmits a control signal called as a beacon at anappropriate time interval, and a mobile terminal capable of receivingthe beacon recognizes the existence of the access point in its vicinity,and further the mobile terminal performs the establishment of aconnection with the access point. On the other hand, because the mobileterminal can recognize the next beacon transmission time by receiving abeacon and by decoding the TBTT field in the beacon, the mobile terminalexisting around the access point sometimes enters its sleep state byturning off the power sources of its receiver until the next TBTT or aplurality of times later TBTT (in a case where no necessity exists forreceiving).

In a case of the infrastructure mode, only the access point transmits abeacon at a predetermined frame period. On the other hand, theperipheral mobile terminal enters the network by receiving the beaconsfrom the access point, and does not transmit any beacons. It is notedthat the present invention principally aims to operate a network withoutintervening by any master controlling station such as the access point,and does not relate to the infrastructure mode directly. Accordingly,the infrastructure mode is not described any more.

<Ad Hoc Mode>

Referring to FIG. 25, the operation in IEEE 802.11 at the time of the adhoc mode on the other hand is described.

In an IBSS of the ad hoc mode, an MT defines an IBSS in a self-organizeddistributed manner after performing a negotiation among a plurality ofmobile terminals. When the IBSS has been defined, the mobile terminalgroup determines TBTTs at every fixed interval after negotiations. Wheneach mobile terminal recognizes the arrival of a TBTT by referring to aclock in a local station, the mobile terminal transmits a beacon in acase where the mobile terminal recognizes that no mobile terminal hastransmitted a beacon yet after a delay of a random time.

In the example shown in FIG. 25, a situation in which two mobileterminals constitute an IBSS is shown. In this case, any one of themobile terminals belonging to the IBSS transmits a beacon every arrivalof a TBTT. Moreover, there is also a case where beacons transmitted fromeach mobile terminal collide with each other.

<Frame Format in IEEE 802.11a>

FIG. 26 shows a configuration example of a frame format prescribed in anextended standard of IEEE 802.11, that is, IEEE 802.11a.

A preamble for indicating the existence of a packet is added to the leadof each packet. In the preamble, a known symbol pattern is defined bythe standard, and a reception side of the packet judges whether thereceived signal is worthy of a preamble or not on the basis of the knownpattern. Then, the reception side can recognize the existence of asignal.

A signal field is defined successively to the preamble. In the signalfield, the information necessary for decoding the information section ofthe packet is stored. The information necessary for decoding the packetis called as a Physical Layer Convergence Protocol header (PLCP header).In the PLCP header, a RATE field indicating a transmission rate of theinformation section (including a Service field being part of the PLCPheader), a LENGTH field indicating the length of the informationsection, a parity bit, a Tail bit of an encoder, a Service field and thelike are included. On the reception side of the packet, the decodingoperations of the subsequent information section can be performed on thebasis of the result of the decoding of the RATE field and the LENGTHfield of the PLCP header.

The SIGNAL field storing the PLCP header has received coding strongagainst noises, and is transmitted at a rate equivalent to 6 Mbps. Onthe other hand, in a packet, the information section is ordinarilytransmitted in a transmission rate mode in which the highest bit ratewithin a range in which errors are generated as little as possible isprovided according to the SNR of a receiver or the like.

In IEEE 802.11a, eight kinds of transmission rate modes of 6, 9, 12, 18,24, 36, 48 and 54 Mbps are defined. Consequently, when atransmitter-receiver is nearly located, a transmission rate mode havinga high bit rate is selected, and there is a case where a communicationstation being located distant cannot decode the information.

The information section is transferred as Physical Layer Service DataUnit (PSDU) to a link layer being an upper layer.

In IEEE 802.11, several frame types are defined. FIG. 27 shows theconfiguration of the PSDU section in each frame of RTS, CTS, ACK andData, which are used in the RTS/CTS procedures described above. RTC andCTS will be described later.

In each frame, a Frame Control field and a Duration field are commonlydefined. The Frame Control field stores the information indicating thekind and the application of the frame, and the like. In specific, theinformation shown in the following table 1 is recorded. TABLE 1 Title ofLength Field [bit] Description Protocol 2 Version Information VersionType/Subtype 6 Identifier Indicating Frame Type ToDS, FromDS 2Identifier Determining the Indication Contents of Each ADDR MoreFragment 1 Flag Indicating the End of Fragment Retry 1 Flag IndicatingResending or not ower Management 1 Flag Indicating Power Management ModeMore Data 1 Flag Indicating the Existence of More Accumulated data WEP 1Flag Indicating the Use of WEP Order 1

In the Duration field, the information of the application (which will bedescribed later) of Network Allocation Vector (NAV) is stored, and atime until the end of the transaction of the packet is recorded.

In the RTS frame, in addition to the above contents, a receiver address(RA) indicating a destination, a transmitter address (TA) indicating atransmission source, and FCS being a check sum exist. Moreover, in theCTS frame and the ACK frame, in addition to the above contents, the RAindicating a destination, and the FCS being a check sum exist.

In the Data frame, in addition to the above contents, four addressfields for specifying a transmission source, a destination communicationstation and the like, a sequence field (SEQ), a Frame Body being the netinformation to be provided to the upper layer, and a Frame CheckSequence (FCS) being a check sum exist.

<Access Control Procedure in IEEE 802.11>

It is necessary to evade contention when a plurality of users performsaccess on the same channel. As a representative communication procedurefor evading contention, Carrier Sense Multiple Access with CollisionAvoidance (CSMA) is known. The CSMA is a connection method forperforming multiple accesses on the basis of carrier detection. Becauseit is difficult in wireless communication to receive a signal which thetransmitter performed its information transmission, collisions areevaded by beginning its own information transmission after thetransmitter has ascertained the nonexistence of the informationtransmissions of the other communication apparatus by the CSMA/CA(Collision Avoidance) system not by the CSMA/CD (Collision Detection)system.

The communication system based on the CSMA/CA is described withreference to FIG. 28. In the shown example, it is supposed that thereare four communication stations #0 to #3 in the communicationenvironment.

Each communication station having transmission data monitors the stateof media for a predetermined frame interval DIFS (DCF (DistributedCoordination Function) Inter Frame Space) from the last detection of apacket. In the case where no media are cleared, namely no transmissionsignals exist, each communication station performs random backoff.Moreover, in a case of no transmission signals exist further in thisperiod, transmission right is given.

In the shown example, the communication station #0 which has set arandom backoff shorter than those of the other neighboring stations canacquire the transmission right to begin a data transmission to thecommunication station #1.

At the time of the data transmission, the transmission sourcecommunication station #0 stores the application information of NetworkAllocation Vector (NAV) in the Duration field of the header of a MACframe (MAC header). In the application information, a time until the endof the transaction of the data communication is recorded.

The communication station #1, which is the transmission destination ofthe data frame, performs a reception operation of the data addressed tothe local station only during the period of Duration recorded in the MACheader. Then, when the data reception is completed, the communicationstation #1 returns an ACK packet to the data source communicationstation #0.

Moreover, when the communication stations other than the datatransmission destination received the data frame, the communicationstations decode the record in the Duration field of the MAC header, andrecognize the state in which the media is occupied without monitoringthe media until the end of the transaction to stop their transmissions.The operation is called such that a neighboring station “sets a NAV”.The NAV becomes valid over a period shown in the Duration field. Forexample, a period until the communication station #1, being thereception destination, returns the ACK packet is assigned as theDuration.

In such a way, according to the CSMA/CA system, a single communicationstation acquires a transmission right while evading contention, andneighboring stations stop their data transmission operations during aperiod of a data communication operation to make it possible to evadecollisions.

However, in a wireless LAN network in an ad hoc environment, it is knownthat a hidden terminal problem is generated. The hidden terminal means acommunication station that, in a case of performing communicationbetween certain specific communication stations, one of thecommunication stations of the communication party can listen but theother communication station of the communication stations cannot listen.Because the hidden terminals cannot perform any negotiation among them,there is the possibility that transmission operation collides with eachother in a case of the above-mentioned CSMA/CA system only.

As a methodology for solving the hidden terminal problem, CSMA/CA(Carrier Sense Multiple Access Collision Avoidance) in accordance with aRTS/CTS (Request To Send/Clear To Send) procedure is known. The IEEE802.11 also adopts the methodology.

Moreover, in the RTS/CTS system, a communication station of a datatransmission source transmits a transmission request packet RTS (requestto send), and starts to transmit data in response to the reception of aconfirmation information packet CTS (clear to send) from a communicationstation of a data transmission destination. Then, when the hiddenterminal receives at least one of the RTS or the CTS, the hiddenterminal can avoid a collision by setting a transmission suspensionperiod of the local station for a period in which data transmissionbased on the RTS/CTS procedure is expected to be performed.

FIG. 29 shows an operation example of the RTS/CTS procedure. In thewireless communication environment, it is supposed that fourcommunication stations #0-#3 exist. The communication station #2 cancommunicate with its neighbor communication apparatus #0. Thecommunication station #0 can communicate with its neighbor communicationstation #1 and #2. The communication station #1 can communicate with itsneighbor communication station #0 and #3. The communication station #3can communicate with its neighbor communication station #3. However, thecommunication station #2 is a hidden terminal for the communicationstation #1, and the communication station #3 is a hidden terminal forthe communication station #0.

After the communication station #0 ascertains in accordance with theprocedure of the CSMA described above that the media are clear for afixed period (from a time T0 to a time T1), the communication station #0transmits an RTS packet to the communication station #1 from the timeT1. In the Type/SubType information in the Frame Control field of theRTS packet, the information indicating that the packet is the RTS isrecorded. In the Duration field, a time until the end of thetransmission-reception transaction of the packet (namely a time until atime T8) is recorded. In the RA field, the address of the destinationcommunication station (the communication station #1) is recorded. In theTA field, the address of the local station (the communication station#0) is recorded.

The transmission rate of each frame of CTS/DATA/ACK, which aretransmitted and received subsequently to the RTS packet, basicallyconforms to the transmission rate mode which is applied in the RTS.

The RTS packet is also received by the communication station #2 locatedin the neighborhood of the communication station #0. When thecommunication station #2 receives the RTS signal, the communicationstation #2 begins its reception operation by finding the preamble, anddecodes the PSDU on the basis of the information obtained by decodingthe PLCP header. Then, the communication station #2 recognizes that thepacket is the RTS packet on the basis of the recorded contents in theFrame Control field in the PSDU, and knows the fact that thecommunication station #0 intends to transmit some information.Furthermore, from the RA field the communication station #2 recognizesthat the local station is not the destination communication station.Then, in order not to prevent the desire of the communication station #0to perform the transmission, the communication station #2 recognizes thestate in which the media are occupied without monitoring the media untilthe transaction ends, and sets the NAV to stop its transmission. The NAVbecomes valid over a period shown in the Duration field, and thecommunication station #2 enters a transmission-disallowed state until atime T8.

On the other hand, the RTS packet is also received by the communicationstation #1, being the destination. When the communication station #1recognizes that the communication station #0 intends to transmit apacket to the local station by decoding the PSDU by the proceduresimilar to the procedure described above, the communication station #1sends back a CTS packet at a time T3 after a frame interval SIFS (ShortInter Frame Space) shorter than an ordinary interval (DIFS).

The transmission rate mode of the CTS packet must be the same as that ofthe RTS. Moreover, in the Frame Control field of the PSDU, a fact thatthe packet is a CTS packet is recorded. In the Duration field, a timeuntil the end of the transaction (namely a time until the time T8) isrecorded. In the RA field, an address of the destination communicationstation (communication station #1) is recorded.

The CTS packet is also received by the communication station #3 locatedin the neighborhood of the communication station #1. The communicationstation #1 decodes the PSDU by the procedure similar to that describedabove, and thereby recognizes that a certain communication station inthe neighborhood schedules the reception of a packet until the time T8.Then, in order not to prevent the desire of the communication station #1to perform the reception, the communication station #3 sets the NAV tostop its transmission until the end of the transmission. The NAV becomesvalid over a period shown in the Duration field, and the communicationstation #3 also enters the transmission-disallowed state until the timeT8 (as described above).

On the other hand, the CTS packet is also received by the communicationstation #0, being the destination. The communication station #0 decodesthe PSDU by the procedure similar to that described above, and therebyrecognizes that the communication station #1 is ready to performreception. Then, the communication station #0 begins to transmit theData packet at a time T5 after a short frame interval SIFS. In the casewhere the transmission of the Data packet ended at a time T6 and thecommunication station #1 could decode the Data packet without anyerrors, the communication station #1 sends back an ACK at a time T7after the interval SIFS. By the fact of the reception of the ACK by thecommunication station #0, the transmission-reception transaction of apacket ends at the time T8.

At the time T8, the communication stations #2 and #3, both beingneighboring communication stations, remove their NAVs, and return totheir ordinary transmission-reception states.

Summarizing this, by the exchanges of the RTS packet and the CTS packet,the neighboring stations of the communication station #0, thetransmission station, are forbidden to perform any transmissions inanswer to the reception of the RTS. The neighboring stations of thecommunication station #1, a reception station, are forbidden to performany transmissions in answer to the reception of the CTS. As a result,without being interrupted by a sudden transmission signal from aneighboring station, the information transmission from the communicationstation #0 to the communication station #1 and the sending back of anACK are performed.

Each communication station in the system performs the transmissionprocedure with using random backoff (setting a time for medium sensingusing random numbers for ascertaining that the media are clear before atransmission) together, and thereby access control by disperse controlis performed.

In the IEEE 802.11, four kinds of packet intervals (IFS: inter framespace) are defined. Hereupon, three IFSs of them are described withreference to FIG. 29. As the IFSs, SIFS (short IFS), PIFS (PCF IFS) andDIFS (DCF IFS) are defined in the order of shortness.

In the IEEE 802.11, as a basic medium access procedure, the CSMA isadopted (as described above). Before a transmitter transmits something,the transmitter operates a timer of the backoff for a random time whilemonitoring a medium state, and the transmission right is not given tothe transmitter until the state of the nonexistence of transmissionsignals during that period is confirmed.

When an ordinary packet is transmitted in accordance with the CSMAprocedure (called as a distributed coordination function (DCF)), themedium state is first monitored only for DIFS after the transmission ofsome packet has been completed. In a case where no transmission signalsexist during the period, the random backoff is performed. Moreover, in acase where no transmission signals exist also during the period of therandom backoff, the transmission right is given to the transmitter.

On the other hand, when a packet having exceptionally high urgency suchas an ACK is transmitted, it is allowed to transmit the packet after theSIFS packet interval. Consequently, a packet having high urgency can betransmitted before a packet to be transmitted in accordance of theordinary CSMA procedure.

In short, the reason why different kinds of packet interval IFS's aredefined is that the priority setting of the transmission rightcompetition of packets is performed according to which one of the SIFS,the PIFS and the DIFS the IFS is, namely according to the length of thepacket interval. For what object the PIFS is used will be describedlater.

<Prioritized Transmission in IEEE 802.11>

IEEE 802.11 prepares means for performing bandwidth reservationtransmissions by the communication station's setup of a prioritizedtransmission time zone in a transmission frame. The bandwidthreservation transmission is described.

In access contention based on the CSMA, it is impossible to secure afixed bandwidth with a guarantee. Accordingly, in IEEE 802.11, amechanism for securing a bandwidth with a guarantee and a PointCoordination Function (PCF) exist.

The PCF is realized on the basis of polling, and the PCF is implementedby locating a control station to be a coordinator in the systemsimilarly to the access control by TDMA such as HIPERLAN/2 and IEEE802.15.3.

FIG. 32 shows an operation example of the PCF. In the example shown inthe same drawing, a case where the communication station #0 operates asan access point (AP) and the communication stations #1 and #2 enter theBSS managed by the AP is supposed. Then, it is also supposed that thecommunication station #1 guarantees a bandwidth to perform thetransmission of information.

After the communication station #0 has transmitted, for example, abeacon, the communication station #0 performs poling to thecommunication station #1 after the interval SIFS further passed (CF-Pollin the drawing). The transmission right of data is given to thecommunication station #1, which has received the CF-Poll, and thecommunication station #1 is permitted to transmit the data after thepassage of the interval SIFS. Accordingly, the communication station #1transmits the data after the SIFS.

When the communication station #0 sends back an ACK to the transmissiondata and a single transaction has ended, the communication station #0performs the polling to the communication station #1 again. In the shownexample, the polling at this time has failed owing to some reason. Inthis case, when the communication station #0 recognizes that noinformation has been transmitted from the communication station #1 evenif the interval SIFS has passed after the polling, the communicationstation #0 regards the situation as one in which the polling has failed,and performs the polling again after the passage of the interval PIFS.When the polling has succeeded, the data is transmitted from thecommunication station #1, and an ACK is sent back.

For example, even if the communication station #2 holds a transmittedpacket during the series of procedure, because the communication station#0 or #1 performs a transmission with the interval SIFS or PIFS beforethe passage of the time interval DIFS, there is no chances of thetransfer of the transmission right to the communication station #2, thecommunication station #1, which has received Polling, always has aprioritized right.

These access periods by the PCF are located in the transmission framewith an object of, for example, regular data deliveries. For example, asshown in FIG. 32, APs frequently periodically locate the PCF.

[Non-patent document 1]

International Standard ISO/IEC 8802-11:1999(E) ANSI/IEEE Std 802.11,1999 Edition, Part II: Wireless LAN Medium Access Control (MAC) andPhysical Layer (PHY) Specification

[Non-patent document 2]

ETSI Standard ETSI TS 101761-1 V1.3.1 Broadband Radio Access Networks(BRAN); HIPERLAN Type 2; Data Link Control (DLC) Layer; Part 1: BasicData Transport Functions

[Non-patent document 3]

ETSI Standard ETSI TS 101-761-2 V1.3.1 Broadband Radio Access Network(BRAN); HIPERLAN Type 2; Data Link Control (DLC) Layer; Part 2: RadioLink Control (RLC) sublayer

[Non-patent document 4]

Supplement to IEEE Standard for Informationtechnology-Telecommunications and information exchange betweensystems-Local and metropolitan area networks-Specific requirements-Part11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)specifications: High-speed Physical Layer in the 5 GHZ Band

[Non-patent document 5]

C. K. Tho, “Ad Hoc Mobile Wireless Network” (Prentice Hall PTR)

SUMMARY OF THE INVENTION

As described above, as a methodology for providing prioritizedcommunication, it is known to provide a periodical or quasi-periodicaltransmission prioritized period. However, in the case where thearrangement of the communication stations as shown in FIG. 33 issupposed, weak points of the methodology of locating the time zones ofthe prioritized transmissions regularly are exposed. In the exampleshown in the same drawing, it is supposed that each of the communicationstations #0 and #3 operates as a coordinator (AP) and electric wavesarrive at only between respective adjacent communication stations.

An operation example showing problems causable in this case is shown inFIG. 34. Because the communication stations #0 and #3 both operating ascoordinators (AP) are in the state in which they cannot directlycommunicate with each other, they cannot be even synchronized with eachother. Moreover, although these coordinators just grasp the states ofthe communication stations under the control of the local station, butdo not know the behaviors of the other communication stations.Consequently, as shown in FIG. 34, the situation in which mutualinterferences are generated between the communication stations #1 and #2to make it impossible to perform communication can be generated.

In the arrangement configuration of each communication station as shownin FIG. 33, the communication station #0 is located beyond thecommunication range of the communication station #2. Consequently, thedata transmission from the communication station #0 to the communicationstation #1 does not hinder the data transmission from the communicationstation #3 to the communication station #2, and these data transmissionoperations ought to be able to perform in parallel at the same time.

However, in the example shown in FIG. 34, because the prioritizedtransmission (PCF) period of the communication station #3 has begunprior to the prioritized transmission (PCF) period of the communicationstation #0, the communication station #1 enters atransmission-disallowed state for suppressing the interference to thecommunication station #2, and cannot answer the calling out from thecommunication station #0. Furthermore, owing to the interference fromthe communication station #1, the communication station #1 cannotreceive any signals from the communication station #0. Consequently, theband cannot be efficiently utilized, and the accommodation ofprioritized traffic is difficult.

The present invention took the technical problem described above intoconsideration. The principal object of the invention is to provide anexcellent wireless communication system, a wireless communicationapparatus, a wireless communication method and a computer program, allenabling a wireless network to be suitably managed by making eachcommunication station perform autonomous distributed communicationoperations.

The present invention further provides an excellent wirelesscommunication system, a wireless communication apparatus, a wirelesscommunication method and a computer program, all enabling eachcommunication station to suitably perform medium access control by theCSMA system or the TDMA system.

Moreover, the present invention provides an excellent wirelesscommunication system, a wireless communication apparatus, a wirelesscommunication method and a computer program, all enabling eachcommunication station to perform communication using a guaranteedbandwidth by providing a prioritized utilization region while evadingmutual interferences.

Moreover, the present invention provides an excellent wirelesscommunication system, a wireless communication apparatus, a wirelesscommunication method and a computer program, all capable of eliminatingunnecessary transmission waiting operation and using a bandwidthefficiently while accommodating prioritized traffic in a wirelessnetwork.

The present invention was made in consideration of the problem. A firstaspect of the invention is a wireless communication system in which eachcommunication station sets a prioritized utilization region to performframe transmission with priority. In the communication system, eachcommunication station cancels a transmission-disallowed state and sendsback a frame responding to a prioritized transmission frame addressed toa local station in answer to reception of the prioritized transmissionframe in a prioritized utilization region of a neighboring stationduring a period of waiting a transmission on the basis of detection of asignal.

It should be noted that the “system” used in this specification means alogical collection of a plurality of apparatus (or functional modulesrealizing specific functions) and does not specifically refer to whetheror not each apparatus or function module is accommodated in a singlehousing.

In the wireless communication system according to the present invention,no coordinators are especially disposed. Each communication stationinforms of beacon information, and thereby let the other neighboringcommunication stations (i.e. within a communication area) its ownexistence. Each communication station notifies the other communicationstation of a network configuration. Moreover, a communication station toanew enter a communication area of a certain communication station candetect a rush into the communication area, for example, by receiving abeacon signal, and can know a network configuration by decodinginformation recorded in the beacon.

In such a case, when there are no communication stations therearound,the communication station can begin to transmit beacons at suitabletiming. Subsequently, a communication station anew entering thecommunication area sets its own beacon transmission timing so that thebeacon should not collide with an existing beacon arrangement. In thiscase, because each communication station acquires a prioritizedutilization region immediately after a beacon transmission, a beaconarrangement is performed in accordance with an algorithm forsequentially setting beacon transmission timing of a newly enteredstation at the almost middle timing of the beacon interval set by theexisting communication stations. Alternatively, the beacon transmissiontiming of a newly entered station is set at a vacant time of the beaconinterval set by the existing communication stations in view of thetransmission traffic quantity of the station.

In a general access contention system by the CSMA, each communicationstation monitors the state of a transmission path. Then, when notransmission signals exist among the transmission paths, eachcommunication station acquires a transmission right. On the other hand,according to the present invention, each communication station sets atransmission prioritized period in a frame period, and performs a datatransmission in which a band is guaranteed. For example, a beacontransmission station can perform a transmission with a shorter frameinterval in its transmission prioritized period immediately after abeacon transmission, and the other communication stations can perform atransmission after a backoff over a frame interval equal to or longerthan that of the beacon transmission station and a random time.

In this case, the priority setting in a contention for the transmissionright of a packet is performed according to the length of a frameinterval, and consequently a communication station which has set ashorter frame interval can inevitably acquire the transmission right.Consequently, by performing the transmission of the packet with a frameinterval shorter than that of the other communication stations over atransmission prioritized period having a length according to a bandquantity required by an upper layer after the beacon transmission, thecommunication station can execute a series of communication procedurewithout being hindered by neighboring stations. Consequently, a softerQoS management can be realized.

However, in a case of setting the prioritized traffic in such acommunication system for performing random access on the premise of theCSMA procedure, or further in case of setting the prioritized traffic bythe TDMA system, there is a problem in which the transmissionprioritized period set by a communication station sometimes does notoperate validly.

For example, in a case where communication stations neighboring to eachother operate under the control of a communication station being ahidden terminal to each other to set a transmission prioritized periodindependent of each other, or in a case where transactions by theRTS/CTS system are simultaneously begun from communication stationsbeing hidden terminals to each other, a situation in which communicationcannot performed because an interference is regarded to be caused iscreated, though respective transmission prioritized periods can besimultaneously operated in parallel in a normal situation. That is tosay, owing to a transaction on one side which transaction has begunpreviously on the basis of the set value of backoff or the like, thetransaction on the other side sets a transmission stopping period,though being in a transmission prioritized period, and the transactionon the other side does not operate well (see FIG. 34).

On the other hand, according to the present invention, although acommunication station enters a transmission-impossible state in responseto a detection of a signal addressed to another station on the basis ofthe medium access control by the CSMA, the communication station cancancel the transmission-impossible state to send back a frame respondingto a frame transmitted with priority which has been addressed to thelocal station during the transmission waiting and has received.

For example, when the communication station receives a CTS addressed toanother station (e.g. a hidden terminal to the local station) from aneighboring station, the communication station sets a NAV to enter thetransmission-disallowed state. When the communication station receivesan RTS frame which is addressed to the local station and has beentransmitted from another neighboring station by utilizing a transmissionprioritized period during the transmission waiting period, thecommunication station cancels the transmission-disallowed state to sendback a CTS frame. Thereby, the communication station can effectivelyoperate the transmission prioritized period.

Moreover, in a case where a communication station cancels thetransmission-disallowed state, the communication station judges thatthere is the possibility that some problem is generated in a time zoneenabling prioritized reception, and determines to begin a searchprocedure. Through the search procedure, the communication stationexecutes the processing of evading the duplication of transmissionprioritized periods.

For example, in a case where a second communication station recognizesthat a signal from a third communication station is received in a timezone in which a transmission using a prioritized utilization region isperformed from a first communication station to the second communicationstation, the second communication station determines to begin the searchprocedure, and transmits a first message requiring the thirdcommunication station to report its reception state. Then, the thirdcommunication station sends back a second message including theinformation pertaining to the communication stations being intransmission-reception states by means of the prioritized utilizationregion in response to the first message.

Then, for evading the duplication of the prioritized utilizationregions, the second communication station transmits a third message tothe first communication station which third message requests the evasionof the transmission in the time zone which is record in the secondmessage and in which the third communication station performstransmission and reception using the prioritized utilization region. Tothe third massage, the first communication station changes thetransmission time zone addressed to the second communication station inresponse to the third message, and thereby the duplication of theprioritized utilization regions is evaded.

Now, the system may be adapted so that the second communication stationextracts only entries of the communication stations which are notrecognized by the local station on the basis of the second message andtransmits the third message to the first communication station whichthird message requests the restraint of transmissions in the time zonesincluded in the extracted entries.

Moreover, the system may be adapted so that, after the firstcommunication station has ascertained the vacant states of media by thedetection of signals, the first communication station changes thetransmission time zone addressed to the second communication station.

Moreover, the system may be adapted so that, after the firstcommunication station has changed the transmission time zone in responseto the third message, the first communication station may send back afourth message to the second communication station which fourth messagereports a result of the change with regard to whether the firstcommunication station could satisfy the request recorded in the thirdmessage or not. To the fourth message, the second communication stationjudges the propriety of the generation of a future new first message onthe basis of the contents of the fourth message.

Moreover, the system may be adapted so that the second communicationstation transfers the fourth message to the third communication stationin a case where the second communication station could not satisfy therequest recorded in the third message. To the fourth message, the thirdcommunication station judges the propriety of the generation of a futurenew first message on the basis of the contents of the fourth message.

Moreover, the system may be adapted so that the first communicationstation stops the transmission operation at least in a part of theprioritized utilization region to the second communication station in acase where the first communication station cannot satisfy the requestrecorded in the third message from the second communication station.Alternatively, the system may be adapted so that the first communicationstation utilizes at least a part of the prioritized utilization regionto the second communication station in a transmission operationaddressed to a station other than the second communication station.

Moreover, as another way of coping with the case of judgment of theexistence of the possibility of the generation of some problem in thetime zone enabling prioritized reception, the system may be adapted sothat the second communication station transmits the second messageincluding the information pertaining to communication stations in thetransmission-reception state to the third communication station by meansof the prioritized utilization region. In this case, the thirdcommunication station transmits a third message to a fourthcommunication station to be a communication partner of the localstation. The third message requests the evasion of the transmission inthe time zone which is recorded in the second message and in which thesecond communication station performs transmission and reception bymeans of the prioritized utilization region. Then, the fourthcommunication station changes the transmission time zone addressed tothe third communication station in response to the third message.

Now, the system may be adapted so that the third communication stationextracts only entries of the communication stations which are notrecognized by the local station on the basis of the second message andtransmits the third message to the fourth communication station whichthird message requests the restraint of transmissions in the time zonesincluded in the extracted entries.

Moreover, the system may be adjusted so that, after the fourthcommunication station has ascertained the vacant states of the media bythe detection of signals, the fourth communication station changes thetransmission time zone addressed to the second communication station.

Moreover, the system may be adapted so that, after the fourthcommunication station has changed the transmission time zone in answerto the third message, the fourth communication station sends back thefourth message to the third communication station which fourth messagereports a result of the change with regard to whether the fourthcommunication station could satisfy the request recorded in the thirdmessage or not. In this case, the third communication station can judgethe propriety of the generation of a future new first message on thebasis of the contents of the fourth message.

Moreover, the system may be adapted so that the third communicationstation transfers the fourth message to the second communication stationand the second communication station judges the propriety of thegeneration of a future new first message on the basis of the contents ofthe fourth message in a case where the third communication station couldnot satisfy the request recorded in the third message.

Moreover, the system may be adapted so that the fourth communicationstation stops the transmission operation at least in a part of theprioritized utilization region to the third communication station in acase where the fourth communication station cannot satisfy the requestrecorded in the third message from the third communication station.Alternatively, the system may be adapted so that the fourthcommunication station utilizes at least a part of the prioritizedutilization region to the third communication station in a transmissionoperation addressed to a station other than the third communicationstation.

Moreover, the system may be adapted so that each communication stationpreserves the received time zone of a prioritized transmission framewhich is not addressed to the local station as a transmission-receptiondangerous zone in answer to the reception of the frame.

In such a case, the communication station performing the prioritizedtransmission can transmit a message requesting a report of thetransmission-reception dangerous zone to the partner station of theprioritized transmission, and thereby can receive a message reportingthe transmission-reception dangerous zone which is preserved by thepartner station. Then, the communication station performing theprioritized transmission can set a prioritized utilization region in atime zone other than the transmission-reception dangerous zone on thebasis of the record of the sent-back message to perform the prioritizedtransmission.

Moreover, each communication station can gather thetransmission-reception dangerous zone by receiving the prioritizedtransmission frame from a neighboring station, and the system may beadapted so that each communication station informs the acquiredinformation pertaining to the transmission-reception dangerous zone tothe neighboring station. In such a case, when each communication stationtries to perform a frame transmission, the communication station canprevent collisions previously by performing the frame transmission inthe way of avoiding the transmission-reception dangerous zones recordedin the information signal received from the transmission destination.

Moreover, a second aspect of the present invention is a computer programdescribed in a computer readable format for executing the processing toset a prioritized utilization region for performing a frame transmissionwith priority on a computer system. The program includes:

-   -   a step of waiting a transmission on the basis of signal        detection;    -   a step of removing a transmission-disallowed state and sending        back a frame responding to a prioritized transmission frame        addressed to a local station in response to reception of the        prioritized transmission frame in a prioritized utilization        region of a neighboring station during a period of waiting a        transmission;    -   a step of judging that there is a possibility that some problem        is generated in the prioritized utilization region in a case        where the transmission-disallowed state is cancelled, and of        determining to begin a search procedure for trying to find a        cause; and    -   a step of executing processing of evading duplication of        transmission prioritized periods through the search procedure.

The computer program according to the second aspect of the presentinvention defines a computer program described in a computer readableformat for implementing predetermined processing on the computer system.In other words, by installing a computer program according to the secondaspect of the present invention in a computer system, a cooperatingaction becomes effective on the computer system, and the computer systemoperates as a wireless communication apparatus. By activating aplurality of wireless communication apparatus like the above to build awireless network, operations and advantages similar to those of thewireless communication system according to the first aspect of thepresent invention can be obtained.

According to the present invention, there can be provided an excellentwireless communication system, a wireless communication apparatus, awireless communication method and a computer program, all enabling awireless network to be suitably managed by letting each communicationstation perform an autonomous distributed communication operation.

Moreover, according to the present invention, there can be provided anexcellent wireless communication system, a wireless communicationapparatus, a wireless communication method and a computer program, allenabling each communication station to perform medium access controlsuitably in accordance with the CSMA system or the TDMA system.

Moreover, according to the present invention, there can be provided anexcellent wireless communication system, a wireless communicationapparatus, a wireless communication method and a computer program, allenabling each communication station to perform communication having aguaranteed bandwidth by providing a prioritized utilization region whileevading mutual interferences.

Moreover, according to the present invention, there can be provided anexcellent wireless communication system, a wireless communicationapparatus, a wireless communication method and a computer program, allenabling the elimination of unnecessary transmission waiting operationsto use a bandwidth efficiently while accommodating prioritized trafficin a wireless network.

Other objects, features and advantages of the present invention willbecome apparent from the preferred embodiments of the present inventionto be described later and the more detailed description given inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view schematically showing a functional construction of awireless communication apparatus operating as a communication station ina wireless network according to a preferred embodiment of the presentinvention;

FIG. 2 is a view for explaining a beacon transmission/receptionprocedure for each communication station in a self-organizeddistribution type network;

FIG. 3 is a view showing a structural example of beacon transmissiontimings (TBTT) arrangeable within a super frame period;

FIG. 4 is a view showing TBTT and actual beacon transmission times;

FIG. 5 a view showing a state in which priority is given to a beacontransmitting station;

FIG. 6 is a view showing a structural example of the super frame (T_SF)in a case of giving a transmission prioritized period (TPP) to thebeacon transmitting station;

FIG. 7 is a view for explaining an operation in which a communicationstation starts transmission in the TPP period and an FAP period,respectively;

FIG. 8 is a view showing a situation that the communication stationtransmits a plurality of virtual beacons, i.e., sub beacons (surplusbeacons) to increase a prioritized utilizing period;

FIG. 9 is a view showing condition transition of the wirelesscommunication apparatus operating as the communication station;

FIG. 10 is a view showing condition transition of the wirelesscommunication apparatus operating as the communication station;

FIG. 11 is a view showing a structural example of a beacon frame format;

FIG. 12 is a view showing a description example of an NBOI;

FIG. 13 is a view showing a situation in which a newly enteredcommunication station sets TBTT of the local station on the basis ofNBOI of each beacon obtained from a beacon received from a peripheralstation;

FIG. 14 is a view showing an example of TBTT set by each communicationstation;

FIG. 15 is a view for explaining a case where the transmissionprioritized period cannot be effectively utilized when each station setsTBTT as in FIG. 14;

FIG. 16 is a view showing an example of a procedure for causing thetransmission prioritized period effectively utilized when each stationsets TBTT;

FIG. 17 is a flowchart showing an operational procedure for canceling acondition of transmission-disallowed by receiving an RTS packet to beprocessed with priority under a condition that the communication stationis in transmission-disallowed due to a carrier detection;

FIG. 18 is a view showing an example of a procedure for causing thetransmission prioritized period effectively utilized when each stationsets TBTT;

FIG. 19 is a view for explaining a searching processing of an open TBTT;

FIG. 20 is a view showing a finally decided beacon arrangement exampleafter carrying out a checking processing and a TBTT changing processingon the beacon arrangement example shown in FIG. 14;

FIG. 21 is a view showing a structural example of a frame format;

FIG. 22 is a view for explaining processing steps for marking atransmission/reception danger zone;

FIG. 23 is a flowchart showing the processing steps for marking atransmission/reception danger zone;

FIG. 24 is a view for explaining processing steps for a case oftransmitting prioritized traffic using sub beacons;

FIG. 25 is a view for explaining an operation of IEEE 802.11 in ad-hocmode;

FIG. 26 is a view showing an example of a frame format in IEEE 802.11a;

FIG. 27 is a view showing a structural example of a frame field definedfor every frame type in IEEE 802.11a;

FIG. 28 is a view for explaining a communication procedure according toCSMA/CA (related art);

FIG. 29 is a view for a medium access procedure according to an RTS/CTS(related art);

FIG. 30 is a view showing a packet interval IFS defined in IEEE 802.11;

FIG. 31 is a view showing an operational example (related art) in whichthe communication station sets a prioritized transmission time zone in atransmission frame to perform bandwidth reservation transmission in IEEE802.11;

FIG. 32 is a view showing an operational example (related art) of PCF;

FIG. 33 is a view for explaining a problem in a case of providing aperiodical or quasi-periodical transmission prioritized period;

FIG. 34 is a view for explaining a problem in a case of providing aperiodical or quasi-periodical transmission prioritized period;

FIG. 35 is a view showing an example of network topology;

FIG. 36 is a structural example of a super frame in the network topologyas shown in FIG. 35;

FIG. 37 is a structural example of a super frame in the network topologyas shown in FIG. 35;

FIG. 38 is a view for explaining an operation of transmitting a beaconat an exceptional timing by the communication station;

FIG. 39 is a view for explaining an operation of transmitting a beaconat an exceptional timing by the communication station;

FIG. 40 is a view for explaining the beacon transmission steps of STA2shown in FIG. 38 and FIG. 39;

FIG. 41 is a view showing an example of network topology;

FIG. 42 is a structural example of a super frame in the network topologyas shown in FIG. 41;

FIG. 43 is a view showing an example of network topology;

FIG. 44 is a view for explaining behaviors of STA3 in accordance withsituations in the network topology shown in FIG. 43; and

FIG. 45 is a view for explaining behaviors of STA3 in accordance withsituations in the network topology shown in FIG. 43.

DESCRIPTION OF PREFERRED EMBODIMENTS

The preferred embodiments of the present invention are described indetail with reference to the drawings.

Communication transmission paths assumed in the present invention arewireless, and a network is built among a plurality of communicationstations. Communication assumed in the present invention is traffics ofa storage switch type, and information is transferred in the unit of apacket. Moreover, in the following description, a single channel issupposed to each communication station, but it is also possible toextend the channel to one using a transmission medium composed of aplurality of frequency channels, i.e. a multi-channel.

A wireless network system according to the present invention has aself-organized distribution type system structure without disposing acoordinator, and executes a transmission control effectively utilizingchannel resources by using a transmission (MAC) frame having a loosetime division multiple access structure. Moreover, each communicationstation can transmit information directly and asynchronously inaccordance with an access procedure based on a carrier sense multipleaccess (CSMA: carrier detection multiple connection) so that aself-organized distribution type wireless network can be configured. Inan embodiment of the present invention, the communication environment isassumed to be IEEE 802.11a being an extended standard of IEEE 802.11,for example.

In such a wireless communication system without particularly disposing acontrolling station as described above, each communication stationnotifies beacon information on a channel to let another communicationstation in the neighbor (i.e., within a communication range) know theexistence of the local communication station and informs of a networkconfiguration. Furthermore, a communication station newly entering acommunication range of a certain communication station can detect itselfentering the communication range by receiving a beacon signal and canknow the network configuration (or enter the network) by decoding theinformation described in the beacon.

The processing in each communication station which processing will bedescribed later is basically the processing to be executed by allcommunication stations entering a network. However, in some cases, notall of the communication stations constituting a network execute theprocessing which will be described in the following.

FIG. 1 schematically shows a functional construction of a wirelesscommunication apparatus operating as a communication station in awireless network according to a preferred embodiment of the presentinvention. The shown wireless communication apparatus 100 can form anetwork while avoiding collisions by effectively performing a channelaccess in the same wireless system.

As shown in the figure, a wireless communication apparatus 100 iscomposed of an interface 101, a data buffer 102, a central control unit103, a transmission data generating unit 104, a wireless transmissionunit 106, a timing control unit 107, an antenna 109, a wirelessreception unit 110, a receive data analyzing unit 112 and an informationstorage unit 113.

The interface 101 exchanges various kinds of information with anexternal apparatus (e.g., a personal computer (not shown) or the like)connected to the wireless communication apparatus 100.

The data buffer 102 is used for temporarily storing data sent from anapparatus connected via the interface 101 or data received via awireless transmission path, before the data is sent out via theinterface 101.

The central control unit 103 performs the management of a series ofinformation transmission and reception processing at the wirelesscommunication apparatus 100 and the access control of a transmissionpath in an integrated manner. In the present embodiment, basically,medium access control based on CSMA or TDMA is performed and the centralcontrol unit 103 can handle prioritized communication with anotherstation. According to the access steps based on CSMA, a backoff timer isoperated for a random time period while monitoring a condition of thetransmission path so that a transmission right is acquired in a casewhere no transmission signals exist during this period.

The transmission data generating unit 104 generates a packet signal anda beacon signal to be transmitted from a local station to a neighboringstation. The term “packet” here includes a transmission requestingpacket RTS of a communication station being a reception destination, anascertainment responding packet CTS to the RTS, an ACK packet and thelike in addition to a data packet. For example, data packet is generatedby cutting out the transmission data stored in the data buffer 102 for apredetermined length to be a payload.

The wireless transmission unit 106 includes a modulator for modulating atransmission signal by a predetermined modulation method such as anOrthogonal Frequency Division Multiplexing (OFDM), a D/A converter forconverting a digital transmission signal to an analog signal, anup-converter for up-converting an analog transmission signal byperforming frequency conversion of the analog transmission signal, apower amplifier (PA) for amplifying the electric power of theup-converted transmission signal, and the like (all being not shown).The wireless transmission unit 106 performs the wireless transmissionprocessing of a packet signal at a predetermined transmission rate.

The wireless reception unit 110 is composed of a low noise amplifier(LNA) for performing the voltage amplification of a signal received fromanother station through the antenna 109, a down-converter fordown-converting the received signal, which has received the voltageamplification, by frequency conversion, an automatic gain controller(AGC), an A/D converter for performing the digital conversion of theanalog received signal, a demodulator for performing synchronizationprocessing for acquiring synchronization and demodulation processing bya demodulating method such as channel estimation and OFDM, and the like(all being not shown).

The antenna 109 wirelessly transmits signals to another wirelesscommunication apparatus on a predetermined frequency channel, orcollects signals transmitted from another wireless communicationapparatus. The present embodiment is configured to have a single antennaand not to perform transmission and reception in parallel.

The timing control unit 107 controls timing for transmitting andreceiving wireless signals. For example, the timing control unit 107performs the control of its own packet transmission timing and thetransmission timing of each packet (such as RTS, CTS, data, ACK and thelike) in accordance with the RTS/CTS system (or the setting of a frameinterval IFS from the reception the packet immediately before to thetransmission of a packet of the local station, the setting of backoff atthe time of a contention transmission, and the like), and the timingcontrol such as the setting of a NAV at the time of the reception of apacket addressed to another station, the transmission and the receptionof a beacon, and the like.

The reception data analyzing unit 112 analyzes a packet signal(including the analysis of a RTS signal and a CTS signal) and a beaconsignal which could be received from another station.

The information storage unit 113 stores an execution procedure commandprogram such as a series of access control operations and the like to beexecuted by the central control unit 103, the information obtained froman analysis result of a received packet and a beacon, and the like. Forexample, the neighboring apparatus information (such as NBOI (which willbe described later)) obtained by the analysis of a beacon is stored inthe information storage unit 113, and the information is suitablyutilized for the control of communication operations such astransmission/reception operation timing, and for beacon generationprocessing.

<B. Establishment of Self-Organized Distribution Type Network Based onBeacon Information Exchange>

In the self-organized distribution type network according to the presentembodiment, each communication station notifies beacon information at apredetermined time interval on a predetermined channel to let anothercommunication station in the neighbor (i.e., in a communication range)know the existence of the local communication station, and informs of anetwork configuration. The present specification defines a transmissionframe period for transmitting a beacon as a “super frame”, and supposesthat it is, for example, 80 milliseconds.

A newly entering communication station can detect that it entered acommunication range, while listening to a beacon signal from aneighboring station by scan operation, and can know the networkconfiguration thereof by decoding the information written in the beacon.Then, while loosely synchronizing with the reception timing of thebeacon, the newly entering communication station sets the beacontransmission timing of the local station at the timing at which nobeacons from the neighboring stations are transmitted.

A beacon transmission procedure at each communication station accordingto the present embodiment will be described with reference to FIG. 2.

Each communication station synchronizes loosely while listening to abeacon transmitted in a neighboring area. When a new communicationstation appears, the new communication station sets its own beacontransmission timing so as not to collide with the beacon transmissiontiming of already existing communication stations.

In a case where there are no communication stations in a neighboringarea, a communication station 01 can start transmitting a beacon at aproper timing. A beacon transmission interval is 80 ms. In an example ofthe uppermost stage shown in FIG. 2, B01 indicates the beacontransmitted from the communication station 01.

Every communication station newly entering the communication rangethereafter sets its own beacon transmission timing so as not to collidewith the arrangement of already existing beacons.

It is assumed for example that a new communication station 02 appears ona channel in which only the communication station 01 exists as shown inthe uppermost stage of FIG. 2. In this case, the communication station02 receives the beacons from the communication station 01 to recognizeits existence and beacon positions, and as shown at the second stage ofFIG. 2, sets its own beacon transmission timing generally at the middleof the beacon interval of the communication station 01 to start beacontransmission.

It is also assumed that another new communication station 03 appears. Inthis case, the communication station 03 receives at least one of thebeacons transmitted from the communication station 01 and thecommunication station 02 to recognize the existence of these alreadyexisting communication stations. As shown at the third stage of FIG. 2,the communication station 03 starts transmission generally at the timingof the middle of the interval of beacons transmitted from thecommunication station 01 and the communication station 02.

Subsequently, each time a new communication station enters an area inthe neighbor in accordance with the similar algorithm, the beaconintervals are narrowed. For example, as shown at the lowermost stage ofFIG. 2, a communication station 04 appearing next sets its beacontransmission timing at generally the middle of the beacon interval setby the communication station 02 and the communication station 01, and acommunication station 05 appearing second next sets its beacontransmission timing at generally the middle of the beacon interval setby the communication station 02 and the communication station 04.

A minimum beacon interval Bmin is defined so that the bandwidth (superframe period) is not get flooded with beacons. Two or more beacontransmission timings are not permitted to be set in Bmin. For example,in a case where the minimum beacon interval Bmin is defined to be 5 msin the super frame period of 80 ms, sixteen communication stations canbe accommodated to the maximum in the range where radio waves can reach.

At the time of arranging a new beacon in the super frame, because eachcommunication station acquires a prioritized utilization region (TPP)just after a beacon transmission (which will be described later), it ispreferable for transmission efficiency that on one channel the beacontransmission timing of each communication station is uniformly dispersedin the super frame period rather than being crowded. Consequently, inthe present embodiment, as shown in FIG. 2, transmission of a beacon isbasically set to be started at an approximately the middle in the timezone in which the beacon interval is longest within a range in which acommunication station can listen by its own.

It is noted that there is another using method in which each piece ofbeacon transmission timing of each communication station is arranged tobe concentrated and reception operation is stopped in the residual superframe period to decrease the power consumption of apparatus.Alternatively, there is also a using method by which beacon transmissiontiming is set the transmission data capacity peculiar to a communicationstation. In the latter case, the communication station sets the beacontransmission timing of the local station to a time (slot) such that theinterval to the next beacon is long when the transmission data quantityis large, but the communication station can set the beacon transmissiontiming to the time such that the interval to the next beacon is shortwhen the transmission data quantity is small. Thereby, a plurality ofcommunication station operating autonomously can effectively use a superframe mutually.

FIG. 3 shows an example of the configuration of beacon transmissiontiming arrangeable in a super frame period. In this example shown inFIG. 3, a lapse of time in the super frame period of 80 ms is drawn as aclock whose hour hand moves on a ring in a clockwise direction.

In the example shown in FIG. 3, sixteen positions 0 to F constitutetimes at which beacon transmission can be performed, namely as slotswhere beacon transmission timing can be arranged. As described withreference to FIG. 2, it is assumed that beacons are disposed inaccordance with the algorithm that beacon transmission timing of newlyentering stations is sequentially set generally at the middle of abeacon interval set by already existing communication stations. If Bminis set to 5 ms, beacons can be arranged in one super frame up to 16 tothe most. That is to say, 16 or more communication stations cannot enterthe network.

Although it is not clearly shown in FIGS. 2 and 3, each beacon istransmitted at a time including an intentional offset by a short timefrom a target beacon transmission time (TBTT), which is the transmissiontime of each beacon. The offset is called “TBTT offset”. In the presentembodiment, the value of the TBTT offset is determined by usingpseudorandom numbers. The pseudorandom numbers are determined by auniquely determined pseudo-random sequence TOIS (TBTT offset indicationsequence), and the TOIS is updated every super frame period.

FIG. 4 shows TBTTs and actual beacon transmission times. As shown in thedrawing, in a case where TBTT offsets are defined to be any one of timesof TBTT, TBTT+microseconds, TBTT+40 microseconds, TBTT+60 microseconds,TBTT+80 microseconds, TBTT+100 microseconds and TBTT+120 microseconds, aTBTT offset at which transmission is performed is determined to everysuper frame period, and the TOIS is updated. Moreover, in a case where atransmission cannot performed at the time at which the transmissionstation has intended to perform the transmission, all zeros or the likeare stored in the TOIS.

By providing the TBTT offset, actual beacon transmission times can beshifted from each other even in a case where two communication stationsarrange their beacon transmission timing in the same slot on a superframe. Even if beacons collide with each other in a certain super frameperiod, each communication station can listen to mutual beacons (orneighboring communication stations can listen to the beacons of both ofthem) in another super frame period. The communication stations notifythe neighboring stations of the beacon information including TOIS setevery super frame period (notification will be described later).

Moreover, in the present embodiment, when each communication stationdoes not perform the transmission and reception of data, eachcommunication station has the obligation of performing a receptionoperation before and after a beacon which the local station transmits.Moreover, even if each communication station does not perform thetransmission and reception of data, each communication station also hasan obligation of operating its receiver continuously for one super frameonce for several seconds to perform a scanning operation, and thereby ofascertaining whether the existence of the peripheral beacons has changedor not, or whether the TBTT of each peripheral station has shifted ornot. Then, when each communication station ascertains a shift in theTBTT, each communication station defines TBTTs defined within a range of−B min/2 milliseconds on the basis of the TBTT group recognized by thelocal station as “being advanced”, and TBTTs defined within a range of+B min/2 milliseconds as “being retarded”. Then, time is modifiedaccording to the most retarded TBTT.

<C. Accessing procedure in self-organized distribution type network>

The wireless communication apparatus 100 operating as a communicationstation performs transmission control using a transmission channeleffectively by means of a transmission (MAC: medium access control)frame having a loose time division multiple access structure, orcommunication operation such as random access based on CSMA/CA in acommunication environment in which no specific controlling stations aredisposed.

Although each communication station transmits beacons at a constantinterval in the present embodiment, the station having transmitted thebeacon is assigned transmission priority during some period after thebeacon was transmitted. Thereby, comings and goings of signals aremanaged to be distributed in a self-organized manner for securing acommunication bandwidth (QoS). FIG. 5 shows how the priority is assignedto the station having transmitted a beacon. This prioritized section isdefined as a transmission prioritized period (TPP) in the presentspecification.

FIG. 6 shows an example of the structure of a super frame period (T_SF)in a case where the transmission prioritized period (TPP) is given tothe station transmitting a beacon. As shown in FIG. 5, after eachcommunication station has transmitted a beacon, a TPP is assigned to thecommunication station having transmitted the beacon. A sectionsucceeding to the TPP is defined as a fairly access period (FAP), andcommunication is performed between communication stations by theordinary CSMA/CA system. Then, the FAP ends at the timing oftransmitting of a beacon from the next communication station, and afterthat, TPPs and FAPs of beacon transmission stations similarly continue.

Each communication station basically transmits a beacon once in everysuper frame period. But, according to circumstances, each communicationstation is permitted to transmit a plurality of beacons or signalssimilar to beacons, and can acquire a TPP every transmission of abeacon. In other words, each communication station can secure resourcesfor prioritized transmission according to the number of beaconstransmitted every super frame period. Hereupon, a beacon which acommunication station transmits without fail at the head of a superframe period is called “normal beacon”, and the second and followingbeacons transmitted at the other timing for TPP acquirement or withanother object are called “sub beacons (surplus beacons)”.

FIG. 7 illustrates operation of a communication station for startingtransmission in a TPP and a FAP respectively.

In the TPP, after the communication station has transmitted a beacon ofthe local station, the communication station can start its transmissionafter a shorter packet interval SIFS. In the shown example, the beacontransmission station transmits an RTS packet after the SIFS. Then, alsoafter that, each of the transmitted packets CTS, data and ACK istransmitted with the packet interval SIFS similarly. Thereby, a seriesof communication procedures can be executed without being hindered byany neighboring stations.

On the other hand, in the FAP, the beacon transmission station startsits transmission after waiting for LIFS+random backoff similarly to theother neighboring stations. In other words, transmission right isuniformly given to all of the communication stations due to the randombackoff. In the shown example, after a beacon of another station hasbeen transmitted, first the medium state is monitored only for the LIFS.In a case where the medium is in a clear condition, that is, notransmission signals exist, during this period, random backoff isperformed. Furthermore, in a case where no transmission signals existalso in this period, the RTS packet is transmitted. The series of thepackets CTS, data, ACK and the like, which are transmitted by beingcaused by the RTS signal, are transmitted with the packet interval SIFS.Thereby, the series of communication procedures can be executed withoutbeing hindered by the neighboring stations.

According to the signal traffic management method described above, acommunication station having high priority sets a shorter frameinterval, and thereby the communication station can acquire aprioritized transmission right.

However, the transmission prioritized period TPP is fixed to a fixedperiod equal to the minimum beacon interval or decided in a time unitdefined in another way. After that, the communication system shifts to aperiod called as the FAP, in which all of the communication stationsobtain a communication right in an even condition including common IFSsand random backoff. Consequently, in a case where a communicationstation becomes in need of a communication band exceeding thetransmission prioritized period TPP obtained by a time of beacontransmission every super frame in conformity with a request from anupper layer, for example, the communication station is adapted to beable to transmit a sub beacon besides a normal beacon and furtheracquire a TPP.

FIG. 8 shows a state in which a communication station transmits aplurality of virtual beacons called as sub beacons to increase theprioritized utilization periods. In the shown example, the communicationstation #1 finds a vacant beacon slot in a super frame for securing acommunication band requested by an upper layer, and obtains a pluralityof TPPs in one super frame by locating the sub beacons of the localstation. Because in a system building super frames in a self-organizeddistributed manner by exchanges of NBOI information, vacant beacon slotscan be searched for also in view of a hidden terminal problem, anacquisition method of the bandwidths using the sub beacons is easy.

Moreover, because the sub beacons are transmitted with an objectdifferent from that of the beacons in a normal situation aimingnotification of network information and the like, the sub beacons arenot always required to include the information same as that included inthe beacons in a normal situation, and it is sufficient as the subbeacons to be signals recording that “they are frames having thepriority different from that of the ordinary frames”. Furthermore, theframes are not even required to be beacons, only the description in acontrol signal frame including RTS, ACK, or the like and a data frameindicating that “the packets has the priority different from that of anordinary packet” sufficiently satisfies the object. The information andthe frame configuration of the beacons in a normal situation will bedescribed later.

FIG. 9 shows a state transition diagram of the wireless communicationapparatus operating as communication stations in the present embodiment.In the shown example, two states are defined. One of the states is a“prioritized transmission mode” equivalent to a TPP period during whichthe local station acquires a prioritized transmission right. The otherof the states is an “ordinary transmission mode” equivalent to an FAPperiod in which all of the communication stations do not obtain anyprioritized transmission right.

In the ordinary operation mode, a communication station begins atransmission after waiting for LIFS+random backoff.

Now, after a beacon transmission timing TBTT of the local station hasarrived and a communication station has transmitted a beacon, thecommunication station transits to the prioritized transmission mode, andacquires the transmission prioritized period TPP.

In the prioritized transmission mode, by performing a transmission withthe frame interval SIFS, a communication station can acquire atransmission right without being hindered by any neighboring stations.

The communication station continues the prioritized transmission modeduring the transmission prioritized period TPP having a lengthequivalent to a bandwidth quantity requested by the upper layer.

Then, when the TPP has ended and the communication station enters theFAP, or when the communication station receives a beacon of anotherstation, the communication station returns from the prioritizedtransmission mode to the ordinary operation mode.

Moreover, FIG. 10 shows another example of the state transition diagramof a wireless communication apparatus operating as a communicationstation. In the shown example, a state is defined which is called as a“prioritized transmission mode” equivalent to the transmissionprioritized period TPP of the another station in addition to the“prioritized transmission mode” equivalent to the TPP period duringwhich the local station acquires a prioritized transmission right andthe “ordinary transmission mode” equivalent to the FAP period duringwhich all communication stations do not obtain any prioritizedtransmission rights.

In the ordinary operation mode, the communication station waits for aperiod equal to the summation of the ordinary frame interval MIFS andrandom backoff before beginning a transmission. During the FAP period,all of the communication stations in the system perform transmissionswith the interval of MIFS+backoff.

Now, after the arrival of the beacon transmission timing TBTT of thelocal station and the transmission of a beacon, the communicationstation transits to the prioritized transmission mode, and acquires thetransmission prioritized period TPP.

In the prioritized transmission mode, by the transmission after only thewaiting time of the frame interval SIFS shorter than the MIFS, thecommunication station can acquire a transmission right without beinghindered by any neighboring stations. The communication stationcontinues the prioritized transmission mode for the transmissionprioritized period TPP having a length equivalent to the bandwidthquantity requested from the upper layer. Then, when the TPP has endedand the communication station enters the FAP, the communication stationreturns to the ordinary transmission mode.

Moreover, when the communication station receives a beacon from anotherstation and the communication station rushes into the transmissionprioritized period of the other communication station, the communicationstation transits to its non-prioritized transmission mode. In thenon-prioritized transmission mode, the communication station waits for aperiod equal to the summation of a frame interval LIFS, which is furtherlonger than the frame interval MIFS at the time of the ordinarytransmission mode, and random backoff before beginning a transmission.

Then, when the TPP of the other station has ended and the communicationstation entered the FAP, the communication station returns to theordinary transmission mode.

D. Frame Format of Beacon

FIG. 11 shows an example of the configuration of the format of a beaconframe which is transmitted in a wireless communication system accordingto the present embodiment.

A beacon includes a Receiver Address (RA) field being an addressuniquely indicating a reception object station, a Transmitter Address(TA) field being an address uniquely indicating a source station, a Typefield indicating the kind of the beacon, a Neighboring Beacon ActivityInformation/Neighboring Beacon Offset Information (NBAI/NBOI) fieldbeing the information of the reception time of the beacon which can bereceived from peripheral stations, a TBTT Offset Indication Sequence(TOIS) field being the information indicating the TBTT offset value(described above), an ALERT field storing various kinds of informationwhich are to be transmitted such as a change of the TBTT and so forth, aTxNum field indicating the quantity of the resources with prioritysecured by the station, a Serial field in which each beacon transmittedin the super frame is exclusively and uniquely numbered as the serialnumber of the beacon, a Sense Level field indicating the signaldetection ability level of the station, a NetID field indicating thelogical network to which the station belongs, a Timing SynchronizationFunction (TSF) field notifying of the time information which the stationcontains therein independent of the access control, and the like.

Moreover, although there are also fields notifying of the otherinformation in the beacon frame, these frames have no direct connectionwith the subject matter of the present invention, and accordingly theyare described as ETC fields. In the ETC fields, the information such aspaging information for a specific station having a schedule of datatransmission immediately after the beacon transmission is sometimesincluded.

In the Receiver Address (RA) field, because a beacon is ordinarilynotifying information, a broadcast address is stored. However, in a casewhere a beacon is transmitted as a sub beacon with an object ofbandwidth securing, the RA field sometimes indicates a receptiondestination station uniquely.

In the Transmitter Address (TA) field, an address uniquely indicatingthe local station is stored.

In the Type field, the kind of the beacon is stored, and is shown theinformation for identifying whether the beacon is a normal beacon, whicheach communication station once transmits during each super frame orwhether the beacon is a sub beacon transmitted for obtaining aprioritized transmission right. Moreover, in a case of the sub beacon,the priority of the traffic provided by the sub beacon is mapped. Forexample, in a case where values are assigned in a way in which a value255 indicates a normal beacon and values 0-254 are mapped as thepriority values of a sub beacon, the normal beacon is recognized as themaximum priority.

In the NBOI field, there is described the positions (reception times) ofbeacons where the local station can receive the beacons as relativepositions from the transmission time of the normal beacon of the localstation in the form of a bitmap. For example, as shown in FIG. 12,stations are accommodated up to 16 in one super frame, the NBOI field iscomposed of 16 bits. Moreover, in the NBAI field, there is described theinformation specifying a “beacon by which the local station actuallyperforms reception processing” in a format similar to that in the NBOIfield.

FIG. 12 shows a description example of the NBOI. In NBOI, each of thecommunication stations O-F sets TBTT in each slot capable of containing16 stations at maximum, composed of 16 bits equivalent to the number ofbeacons arrangeable in a super frame. In the example shown in thefigure, the communication station 0 produces an NBOI field of“1100,0000,0100,0000”. This indicates that the communication station 0shown in FIG. 3 notifies that “the beacons from the communicationstations 1 and 9 can be received” in the communication environment. Thatis to say, in a case where a beacon can be received related to each bitof the NBOI corresponding to the relative position of a received beacon,a mark is allotted, and in a case where the beacon is not received, aspace is allotted. Moreover, the reason why the MSB is 1 is that thelocal station transmits a beacon, and the place corresponding to thetime when the local station transmits the beacon is also marked.

When each communication station receives mutual beacon signals on acertain channel, the communication channel can avoid the collisions ofbeacons on a channel while arranging its own beacon transmission timing,or while detecting the receiving timing of a beacon from a neighboringstation on the basis of the description of NBOI included in the beaconsignals.

In the TOIS field, a pseudo-random sequence for determining the TBTToffset is stored, and the pseudo-random sequence indicates the quantityof the TBTT offset with which the beacon is transmitted. In therelationship between the TBTT and the actual beacon transmission time,for example as shown in FIG. 4, in a case where an actual beacontransmission time is defined as any one of the times of TBTT, TBTT+20microseconds, TBTT+40 microseconds, TBTT+60 microseconds, TBTT+80microseconds, TBTT+100 microseconds and TBTT+120 microseconds, eachcommunication station selects the shift quantity from the TBTT at thetime of the transmission of this time before the beacon transmission byupdating the TOIS, and determines an actual beacon transmission time.Moreover, in a case where the transmission station cannot perform thetransmission at an intended time, the transmission station stores allzero or the like in the TOIS, and transmits to a beacon receptionstation the information indicating that the beacon transmission timingat this time was not performing at an intended time.

In the Delay field, in a case where the beacon is transmitted with adelay from a scheduled transmission time owing to some cause, a valueindicating how much the beacon was delayed from the TBTT to betransmitted (Delay value) is stored. As the causes of the delay of thetransmission time of a beacon, there are considerable a cause of thenecessity of detecting transmission signals of the other stations forevading collisions, and the other external causes. The communicationstation which has received the beacon can know the TBTT in which thebeacon is accommodated in a normal situation by referring to the Delayfield even in a case where the beacon was not transmitted at thescheduled time on the basis of the TBTT and the TBTT offset.

It is noted that, by writing the Delay value into the TOIS field, theframe length of a beacon can be saved. For example, the Delay field isexpressed by a flag of one bit, and the TOIS field is defined such that,in a case where the Delay flag is 0, an ordinary TOIS is recorded in theTOIS field, and that, in a case where the Delay flag is 1, a Delay valueis recorded in the TOIS field.

In the ALERT field, information which is to be transmitted toneighboring stations in an abnormal state is stored. In specific, in acase where a change of the TBTT of the normal beacon of the localstation is scheduled, the schedule is described. Moreover, in a casewhere the stop of the transmission of sub beacons is requested to theneighboring stations, the request is described.

In the TxNum field, there is described a value equivalent to an hourrate at which the station secures the resources with priority by othermeans to perform a transmission. To put it concretely, the number of thesub beacons which the station transmits for securing the resources withpriority is described.

In the Serial field, as the serial number of the beacon, an exclusivenumber unique to each of the beacons transmitted in the super frame isdescribed. The information indicating the order of the TBTT in which thebeacon is transmitted on the basis of the normal beacon of the localstation is described.

In the Sense Level field, the information indicating the level of areceived signal (received SINR) to which the station detects as thereceived signal is stored. There is a case where a communication stationlowers the detection accuracy of the preamble in its receiver not toreceive the signals received at a low SINR as received signalsintentionally with an object of controlling the area in which the localstation can perform communication. The field notifies of such a controlsituation in the communication station. On the side of a beaconreception station, the beacon reception station can adjust the data rateaddressed to the beacon source station and can make its own detectionaccuracy of the preamble by referring to the field.

The Network Identifier (NetID) field is an identifier indicating anowner of the beacon transmitting station or the like. A receptionstation can recognize whether the local station and the station belongto the logically same network or not by referring to the field.

The Timing Synchronization Function (TSF) field is a field for notifyingof the time information contained in the beacon transmission station.The time is used chiefly in an object of synchronization of anapplication in the application different from medium access. Independentof the correction of a clock for changing the transmission time of abeacon and for preserving the TDMA structure, or of the access controlof TBTT offset, the TSF field transmission station shows thetransmission time of the signal calculated by free-running faithfully tothe clock equipped by the transmission station. On the side of thereception station of the beacon, the value is sometimes provided to theupper layer of the communication protocol together with the receptiontime, and is preserved as the time information on the basis of theinformation transmitted from the station.

Moreover, Paging information which may possibly be included in the ETCfields is sometimes equivalent to the information equivalent to the RTSshown with respect to the related art of the CSMA. Moreover, not everytime the Paging information exists to the beacons, and there is a casewhere a beacon and the RTS information clearly showing the objectdestination communication station are multiplexed in the same PSDU.

<E. Setting TBTT of Beacon>

After the throwing in of the power source, the communication stationfirst tries to perform a scan operation, namely tries to perform toreceive a signal continuously for a super frame length or longer, andperforms the existence confirmation of a beacon transmitted from aneighboring station. When no beacons have been received from neighboringstations in this process, the communication station sets suitable timingas the TBTT.

On the other hand, in a case where the communication station hasreceived a beacon transmitted from a neighboring station, thecommunication station shifts the NBOI field of each beacon received fromthe neighboring station according to the reception time of the beaconwhile obtaining a logical sum (OR) of them, and refers. Thereby, thecommunication station extracts beacon transmission timing in the timingcorresponding to bit positions which have not been marked, finally. Aseries of 0/1 obtained by referring to the NBOI field of each beaconreceived from peripheral communication stations in the way of OR whileshifting according to the reception time of the beacon is called as areceived NBOI table (Rx NBOI Table).

Because a communication station basically acquires a prioritizedutilization region (TPP) immediately after a beacon transmission, it ispreferable that the beacon transmission timing of each communicationstation is even dispersed in a super frame period in view oftransmission efficiency. Accordingly, the center of a period in whichthe run length of a space becomes longest as a result of obtaining OR ofNBOI obtained from the beacon received from the neighboring stations isdetermined as the beacon transmission timing.

However, in a case where the TBTT interval at which the run lengthbecomes the longest is smaller than the TBTT interval at which the runlength becomes shortest (i.e. a case of being equal to or less thanBmin), a novel communication station cannot enter this system.

FIG. 13 shows a state in which a newly entering communication stationsets the TBTT of the local station on the basis of the NBOI of eachbeacon obtained from the beacons received from the neighboring stations.The NBOI is formed of 16 bits equivalent to the number of beaconscapable of being located in a super frame.

In the example shown in FIG. 13, a newly appeared communication stationA is noticed, and a communication environment in which there arecommunication stations 0, 1 and 2 around the communication station A issupposed. Then, it is supposed that the communication station A couldreceive beacons from the three stations 0 to 2 in a super frame by scanoperation.

The NBOI field describes the receiving times of beacons from theneighboring stations as relative positions to the normal beacon of thelocal station in a bit map format (as described above). Accordingly, thecommunication station A shifts the NBOI fields of the three beaconswhich could be received from the neighboring stations according to thereception time of each beacon to align the corresponding positions ofbits on a time axis, and the communication station A obtains OR of theNBOI bits at each timing to refer.

A series obtained as a result of consolidating the NBOI fields of theneighboring stations to refer is “1101,0001,0100,1000” shown by beingindicated as “OR of NBOIs” in FIG. 13. In the series, 1 denotes arelative position at the timing at which the TBTT has been already setin the super frame, and 0 denotes a relative position at the timing atwhich the TBTT is not set. In this series, the longest run length of aspace (zero) is three, and there are two positions of candidates. In theexample shown in FIG. 13, the communication station A sets the fifteenthbit in the series as the TBTT of the normal beacon of the local station.

The communication station A sets the time of the fifteenth bit as theTBTT of the normal beacon of the local station (namely, the head of thesuper frame of the local station), and starts to transmit a beacon. TheNBOI field transmitted by the communication station A at this time isone describing each reception time of the beacons of the communicationstations 0 to 2 capable of receiving a beacon in the bit map format inwhich the bit position corresponding to the relative position from thetransmission time of the normal beacon of the local station is marked.This NBOI field is the one shown in FIG. 13 as “NBOI for TX (1 BeaconTX)”.

It is noted that, when the communication station A transmits a subbeacon with the object of obtaining a prioritized transmission right orthe like, the communication station A, further after this, searches thelongest run length of the space (zero) of the series shown as “OR ofNBOIs” consolidating the NBOI fields of the neighboring stations, andsets the transmission time of the sub beacon at the place of thesearched out space. In the example shown in FIG. 13, a case where twosub beacons are transmitted is supposed, and the transmission timing ofthe sub beacons is set at the times of the spaces at the sixth bit andthe eleventh bit of “OR of NBOIs”. In this case, the NBOI fieldtransmitted by the communication station A has marks also at the placewhere the local station performs beacon transmission (a relativeposition to the normal beacon) in addition to the relative positionsfrom the normal beacon of the local station and the received beaconsfrom the neighboring stations, and is in the state shown in “NBOI for TX(3 Beacon TX)”.

In a case where each communication station sets the beacon transmissiontiming TBTT of the local station by the above-mentioned processingprocedure and transmits a beacon, the collisions of the beacons can beavoided in the condition in which each of the communication stationsstand still and the arrival ranges of radio waves do not change.Moreover, by transmitting sub beacons (or a signal similar to aplurality of beacons) in a super frame according to the priority oftransmission data, it is possible to assign resources with priority toprovide QoS (quality of service) communication. On assigning aprioritized utilization region, it is possible to evade collision of theprioritized utilization regions in the same manner. Moreover, byreferring to the number of beacons (NBOI fields) received fromperipheral regions, each communication station can autonomously graspthe degree of saturation of the system. Consequently, it becomespossible to perform the containing of a prioritized traffic whileincluding the degree of saturation of the system in every communicationstation, though the system is a disperse control system. Moreover,because beacon transmission times are arranged in order not to collidewith each other by the reference of the NBOI fields of the beaconsreceived by each communication station, the situation in whichcollisions frequently occur can be avoided even if a plurality ofcommunication stations contains prioritized traffics.

F. Transmission-Disallowed Period (Setting and Referring of NBAI)

In a wireless network according to the present embodiment, an NBAI fieldis set in the frame format of a beacon with an object of reducing thehidden terminals of beacon reception. The NBAI field is in a formatsimilar to that of the NBOI field. In the NBAI field, bits are arrangedon the basis of the transmission time of the normal beacon of the localstation, and the information for specifying the TBTT at which the localstation actually performs reception processing is described in a bitmapformat.

Each communication station in its sleep mode state does not receive anybeacons of the other stations. Accordingly, in the sleep mode state, abeacon is transmitted in a state in which all zero is set in the NBAIbits (however, except for the time when the local station performs abeacon transmission). On the other hand, when a communication stationenters a communication state with another station, the communicationstation performs the operation of receiving the normal beacons of theneighboring station. In this case, the beacon is transmitted in a statein which 1 is set in the bits corresponding to the reception times(TBTTs) of the normal beacons of the neighboring station in the NBAIbits.

Incidentally, in a case where the neighboring station uses one or moreprioritized utilization regions because of the transmission of subbeacons, 1 is set in the NBAI bits corresponding to the reception times(TBTTs) of the received sub beacons only in a case where it is judgedthat transmission with priority in the prioritized utilization region isperformed to the local station. Whether the prioritized transmission inthe prioritized utilization region is performed to the local station ornot is judged on the basis of a fact of being in a communication statewith the communication station transmitting the sub beacons or a resultof an advanced negotiation.

Moreover, in a further case where the destination of the data to betransmitted is assigned to every period defined by transmission of a subbeacon by some means, 1 is set in the NBAI bit corresponding to thereception time (TBTT) of the only sub beacon which is judged to be oneaccompanied by the TPP having the data addressed to the local station.That is to say, a communication station judges whether the communicationstation sets 1 to an NBAI bit or not on the basis of whether the subbeacon to be transmitted in the time zone and the signal transmitted byanother station using the TPP are transmitted to the local station ornot (or whether the local station is required to receive the signal ornot).

On the other hand, on the side of the station which has received thebeacon, OR operation is performed while shifting the NBAI bits in thereceived beacon according to the beacon reception time by the procedure(described above) similar to the procedure when the Rx NBOI Table isproduced, and thereby whether a transmission-disallowed processing isperformed or not in each TBTT set in the super frame is judged.

In a case where the result of the OR operation of the NBAI bit at thecorresponding time is 1, the communication station considers lest thebeacon reception of the other stations should be hindered by setting thetransmission-disallowed state over a fixed period defined from the timeof the TBTT, or from a time shortly preceding to the time, to themaximum length of the TBTT offset+the length of the beacon. However, ina case where the TBTT is the beacon transmission time of the localstation, the transmission-disallowed processing is not performed, but aframe including the beacon information is transmitted.

Incidentally, the transmission-disallowed state is canceled byperforming a beacon transmission or a beacon .reception, and the stateis changed to the state of the ordinary transmission and receptionprocessing state.

G. Illustration of Case in which Problem Occurs

Now, a case where four communication stations are located in thesituation shown in FIG. 34 is supposed. In this case, when eachcommunication station transmits beacons in accordance with the proceduredescribed above, there is a case where the beacons of each station aretransmitted as shown in FIG. 14, for example. Incidentally, a case whereTBTTs at eight positions can be set in one super frame is supposed.

In the shown example, a case where a communication station #0 transmitsfour beacons in total in a communication application addressed to acommunication station #1 and a communication station #3 transmits threebeacons in a communication application addressed to a communicationstation #2 is supposed. Among the beacons, the communication station #0and the communication station #3 severally select the same TBTT at thetimes T0, T2 and T5.

In this case, there may be a case where the transmission prioritizedperiods TPP set with an object of performing a transmission withpriority cannot be effectively used. The state is illustrated in FIG.15. In FIG. 15, each portion of the times T0, T2 and T5 in FIG. 14 isshown in enlarged scales.

In a sequence beginning from a time T0, because a TBTT offset of thecommunication station #3 is shorter than a TBTT offset of thecommunication station #0, the communication station #3 first transmits asignal including a beacon and an RTS. In response to the signal, thecommunication station #2 sends back a CTS to the communication station#3. Because the CTS is also received by the communication station #1,the communication station #1 sets a NAV over a Duration periodinstructed in the CTS, and sets a transmission-disallowed period inaccordance with the CSMA/CA procedure.

After that, a signal including a beacon and an RTS addressed to thecommunication station #1, and a signal including RTS information aretransmitted from the communication station #0. Even if the communicationstation #1 can receive the signals, the communication station #1 is inthe transmission-disallowed state, and consequently the communicationstation #1 cannot send back any CTSs. Consequently, this situation leadsto a state in which the transmission prioritized period TPP acquired bythe communication station #0 by the performance of the local station'sbeacon transmission does not work effectively. The state is based on afact that the communication station #0 cannot be concerned in thecommunication stations preceding to the communication station #0 by twohops or more in the management method of the neighboring stations bymeans of the NBOI described above.

Moreover, at a time T2, because the TBTT offsets of the communicationstations #0 and #3 coincide with each other, the data transmission fromthe communication station #0 to the communication station #1 and thedata transmission from the communication station #3 to the communicationstation #2 are simultaneously performed in parallel with each other. Inthis case, to each of the communication stations #0 and #3, thetransmission prioritized periods TPP acquired by the beacon transmissionof each of them effectively work.

On the other hand, at a time T5, because the TBTT offset of thecommunication station #0 is shorter than the TBTT offset of thecommunication station #3, a phenomenon similar to one at the time T0 isproduced. That is to say, at this time, the communication station #2cannot send back any CTS, and the transmission prioritized period TPP ofthe communication station #3 does not work effectively.

H. Coping with Problem (First Solution)

In this item, a description is given to a first solution for growing outof the situation with the best effort in which situation thetransmission prioritized period TPP of a communication station does notwork effectively as shown in FIG. 15. FIG. 16 shows an example of anoperation procedure in this case. Incidentally, reference points such asa time T0 shown in FIG. 16 have nothing to do with those shown in FIG.14 or the like.

H-1. Activation of Search Procedure

The time T0 is a time of TBTTs of the communication stations #0 and #3.Because the value of the TBTT offset at the TBTT of the communicationstation #3 is 0, the communication station #3 performs the transmissionof a beacon including RTS (Paging information) to the communicationstation #2 at the TBTT. At a time T1, the communication station #2 sendsback a CTS in response to the RTS from the communication station #3.

The CTS from the communication station #2 is also received by thecommunication station #1. In an ordinary CSMA operation, thecommunication station #1 sets a NAV by means of the value of Durationshown by the CTS, and enters its transmission-disallowed state. Becausethe communication station #1 recognizes that the time T0 is the TBTT ofa transmission beacon of the communication station #0, and because thecommunication station #1 has not received any beacons from thecommunication station #0 yet, the communication station #1 is in itstransmission-disallowed state except for the time of receiving anemergent signal.

In the present embodiment, in a case where the communication station #1receives the CTS which interferes a prioritized utilization regionstarting at the transmission beacon time from the communication station#0 and requests the setting of a NAV over a long period, thecommunication station #1 stores the address of the source communicationstation of the CTS as a “communication station which should be marked”.Moreover, the communication station #1 stores the time when the CTS wasreceived as a “marked time” at the same time.

After that, when a TBTT offset has passed from the TBTT, at a time T2the communication station #0 performs the transmission of a beaconincluding RTS (Paging information) to the communication station #1, andthe communication station #1 receives the beacon.

At this point, the communication station #1 is in its transmissiondisallowance state owing to the reception of the CTS from thecommunication station #2. But, because the received signal includes bothelements of a beacon and the RTS addressed to the local station, it isfound that the signal is transmitted from a communication stationholding the prioritized utilization region. In this way, thecommunication station #1 judges that the signal transmitted from thecommunication station holding the prioritized utilization region shouldbe processed with priority. That is to say, when the communicationstation #1 receives the RTS which should be processed with priority, thecommunication station cancels the transmission disallowance state whichis presently set, and performs the send back of CTS.

Moreover, when the communication station #1 ascertains the existence ofa communication station registered as a “communication station whichshould be marked” and the “marked time” is not distant from the presenttime more than T_Bmin in a case where the communication station #1canceled the transmission-disallowed state, the communication station #1judges that there is the possibility that some problem has been producedin a time zone in which prioritized reception can be performed, anddetermines to begin a Search procedure. Through the search procedure,the communication station executes the processing of evading theduplication of transmission prioritized periods, and this respect willbe described in detail later.

Incidentally, by the communication station #1's transmission of the CTS,a part of the signal received by the communication station #2 receivesinterference, and it can be produced that a part of the data is damaged.But, because the length of the CTS signal is short, not all of thesignal is damaged.

H-2. Processing Flow Until Activation of Search Procedure

FIG. 17 shows an operation procedure in the form of a flowchart forcanceling the transmission-disallowed state by the reception of an RTSpacket which should be processed with priority when a communicationstation is in its transmission-disallowed state owing to a carrierdetection. The operation procedure shown in the same drawing is actuallyimplemented in the form of the execution of a predetermined run commandprogram by the central control unit 103 in the wireless communicationapparatus 100 operating as a communication station.

When a communication station receives a signal (step S01), thecommunication station first judges whether the signal is addressed tothe local station or not (step S02). When the received signal is judgednot to be addressed to the local station, the communication stationperforms the following processing.

First, the communication station judges whether the received signal hasbeen transmitted with priority or not (step S03). Then, in a case of notwith priority, the communication station clears the informationpreserved as the “communication station which should be marked” (stepS05) before the communication station changes to the ordinary receptionstate. In the example described above, whether the received signal hasbeen transmitted with priority or not is judged on the basis of whetherthe received signal has been received in the local station'stransmission-disallowed state or not.

Moreover, in a case where the received signal is judged to be one whichhas been transmitted with priority (step S03), the communication stationsuccessively judges whether the destination of the received signal is aneighboring station of the local station or not (step S04). Now, whenthe destination of the received signal is judged to be the neighboringstation, the communication station clear the information preserved asthe “communication station which should be marked” (step S05) beforechanges into the ordinary reception state.

On the other hand, when the destination of the received signal is judgednot to be any neighboring stations (step S04), the communication stationstores the transmission source station of the received signal as the“communication station which should be marked” (step S06).

On the other hand, in a case where the received signal is judged to beaddressed to the local station at the step S02, the following processingis performed.

First, whether the received signal has been transmitted with priority ornot is judged (step S07). Then, in a case of not with priority, thecommunication station clears the information preserved as the“communication station which should be marked” (step S12) before thecommunication station changes into the ordinary reception state. In theexample described above, the received signal is judged to be withpriority by ascertaining that RTS accompanies the beacon.

Moreover, in a case where the received signal is judged to be one whichhas transmitted with priority, whether a NAV is presently set in thelocal station or not is further judged (step S08). Here, when the NAV isnot set, the communication station clear the information preserved asthe “communication station which should be marked” (step S12) before thecommunication station changes into the ordinary reception state.

On the other hand, in a case where the NAV is set in the local station(YES is step S09), the communication station cancels the NAV (step S09).Successively, the communication station judges whether the communicationstation holds the information of the “communication station which shouldbe marked” or not (step S10). Now, in a case where the information ofthe “communication station which should be marked” is not preserved, thecommunication station changes into the ordinary reception state. But ina case where the information of the “communication station which shouldbe marked” has been already preserved, the communication stationdetermines to begin the search procedure (step S11), and thecommunication station clears the “communication station which should bemarked” (step S12).

H-3. Details of Search Procedure

FIRST EXAMPLE

After the communication station #1 has determined to begin a searchprocedure by the processing shown in FIG. 17, the communication station#1 exchanges messages between another communication station to executethe processing of evading the duplication in the transmissionprioritized period.

Transmission of First Message

The communication station #1, which has determined to begin the searchprocedure, transmits a request to the communication station #2registered as the “communication station which should be marked” ofreporting a reception situation in the transmission prioritized periodTPP of the communication station #2 as a first message. In the exampleshown in FIG. 16, a Search as the first message is transmitted at thetime T3.

Incidentally, because the communication station #1 has activated thesearch procedures with regard to the communication station #0 and thecommunication station #2, the communication station #1 activates atimer. Then, it is set that the communication station #1 does notactivate a novel search procedure from the local station for a whileafter that, and that the communication station #1 further discards themessages pertaining to the examination procedure from the stations otherthan the object station of the search procedure (the communicationstation #0 and the communication station #2).

Transmission of Second Message

The communication station #2, which has received the first message,makes the information of one record composed of the TBTT of thecommunication station with which the communication station #2 ispresently in a transmission-reception state by using the transmissionprioritized period TPP, and the address of the communication station. Byindicating the TBTT by a relative time from the time of the ordinarybeacon of the communication station #2, time can be informed even if theclock managing the whole system does not exist. Moreover, thecommunication station #2 sends back the made information to thecommunication station #1 as the second message. In the example shown inFIG. 16, the Report as the second message is transmitted at a time T4.

Incidentally, the communication station #2, which has received the firstmessage, recognizes that the search procedure has begun in theneighboring communication station, and activates a timer. Then, it isset that the communication station #1 does not activate a novel searchprocedure from the local station for a while after that, and that thecommunication station #2 further discards the messages pertaining to thesearch procedure from the other stations.

Transmission of Third Message

The communication station #1, which has received the second message,extracts the records pertaining to the stations which the local stationdoes not recognize (hidden terminals to the local station or nextneighboring stations) among the information group stored in the secondmessage, and makes a third message including the TBTT information of theextracted records. By indicating the TBTT by a relative time from thetime of the ordinary beacon of the communication station #1, time can beinformed even if the clock managing the whole system does not exist.Moreover, the communication station #1 transmits the made third messageto the communication station #0. In the example shown in FIG. 16, theAsk as the third message is transmitted at a time T5.

The third message indicates that “there is the possibility that thecommunication station #1 collides with the reception of thecommunication station #2 in the transmission prioritized period TPP inthe TBTT included in the message”. In other words, the third messageindicates to the communication station #0 that there is the possibilitythat a signal addressed to the communication station #1 cannot always bereceived with priority in the TBTT.

Scanning and Change of TBTT

When the communication station #0, which has received the third message,recognizes that there is a problem with regard to the reception in thetransmission prioritized period TPP of the communication station #1, thecommunication station #0 activates the change processing of the TBTT forchanging the transmission time in the TPP addressed to the communicationstation #1.

In the TBTT changing processing, the communication station #0 performsthe scanning processing for the super frame, and searches a vacant TBTTin the time zone which is not recorded in the third message. Then, thecommunication station #0 tries to change the time zone for performing atransmission having a high priority addressed to the communicationstation #1.

Moreover, at the same time when the communication station #0 determinedto perform the scanning processing, the communication station #0 informsthe periphery of a schedule of changing the TBTT of the local station inthe ALERT field of the transmission beacon.

Then, the communication station #0 activates the scanning processing asshown in FIG. 16. When the scanning processing has ended, thecommunication station #0 searches the vacant TBTT by the proceduredescribed above in the consideration of the time zone recorded in thethird message as an NG time zone (which respect will be describedlater), and replaces the TBTT of the beacon performing a transmission inthe NG time zone at the present time. In the example shown in FIG. 16,the TBTT of the communication station #0 is replaced with the time T6.

Transmission of Fourth Message

When sufficient vacant TBTTs exist, the communication station #0 returnsto a state in which the transmission prioritized period TPP can beeffectively used by the processing described above. However, in a casewhere insufficient vacant TBTTs exist, there is the possibility that thecommunication station #0 cannot deal with the request of thecommunication station #1 sufficiently. In a case where the communicationstation #0 performs communication also to another station, thecommunication station #0 schedules the transmission control in orderthat transmissions may be performed to the communication stations otherthan the communication station #1 at the time reported as NG by thecommunication station #1. Alternatively, there is also a case where thetransmission of a sub beacon at the time is stopped.

With an object of informing the communication station #1 of such asituation, the communication station #0 reports the existence of theTBTTs which could not be changed to the communication station #1. It isdesirable to report that all of the TBTTs have been changed as therequest to the communication station #1 even in a case where thecommunication station #0 could deal with the request of thecommunication station #1. The communication station #0 transmits theinformation to the communication station #1 as the fourth message. Inthe fourth message, the NG time at which beacons have still beentransmitted, though which time has been reported as the NG time in thethird message, is clearly described. In the example shown in FIG. 16,Status as the fourth message is transmitted at the time T7.

Transmission of Fifth Message

The communication station #1, which has received the fourth message,grasps how much the communication station #0 has responded the request.In the example shown in FIG. 16, the communication station #1 preservesthe time zone (TBTT) reported as one in which communication station #0could not responded the request by the communication station #0 as an“unsolved time zone”, and takes notice lest the communication station #1should be initiated a search procedure on the basis of a phenomenonproduced in the time zone. Furthermore, the communication station #1transfers the “unsolved time zone” information to the communicationstation #2 as a fifth message for owning the “unsolved time zone”information commonly with the communication station #2, which is in thesimilar state. In the example shown in FIG. 16, Status as the fifthmessage is transmitted at the time T8.

Reception of Fifth Message

The communication station #2, which has received the fifth message,similarly to the communication station #1, preserves the reported timezone (TBTT) as the “unsolved time zone”, and takes notice lest thesearch procedure should be initiated owing to the phenomenon generatedin the time zone.

H-4. Details of Search Procedure

SECOND EXAMPLE

In the procedure described above with reference to FIG. 16, thecommunication station #1 activates the procedure, and performsexamination of the communication station #2 by a Search message. Afterthat, the communication station #1 transmits a TBTT changing request tothe communication station #0 by an Ask message. On the other hand, theobject of the present invention of eliminating the situation in whichtransmission prioritized periods collide with each other can be achievedby a procedure in which the communication station #1 activates theprocedure and the communication station #1 itself notifies thecommunication station #2 of the examination result to make thecommunication station #3 perform the TBTT changing request. Theprocedure in this case is described in the following with reference toFIG. 18.

Transmission of Second Message

The communication station #1, which has determined to begin the searchprocedure by the processing shown in FIG. 17, makes the information ofone record composed of the TBTT of the communication station with whichthe communication station #1 is presently in a transmission-receptionstate by using the transmission prioritized period TPP, and the addressof the communication station. By indicating the TBTT by a relative timefrom the time of the ordinary beacon of the communication station #1,time can be informed even if the clock managing the whole system doesnot exist. Moreover, the communication station #1 transmits the madeinformation to the communication station #2 as the second message. Inthe example shown in FIG. 18, the Report as the second message istransmitted at a time T4. Incidentally, the communication station #1,which has transmitted the second message, and the communication station#2, which has received the second message, recognize that the searchprocedure has begun in the neighboring communication station, andactivate a timer. Then, it is set that the communication stations #1 and#2 do not activate a novel search procedure from the respective localstations for a while after that, and that the communication stations #1and #2 further discard the messages pertaining to the search procedurefrom the other stations.

Transmission of Third Message

The communication station #2, which has received the second message,recognizes that the time zone at which the local station performsprioritized reception coincides with the time zone at which an adjacentstation performs prioritized reception. Then, the communication station#2 determines to request the change of the TBTT to the partner stationperforming the prioritized reception in the time zone included in thesecond message received from the communication station #1. In theexample shown in FIG. 18, as a partner station performing theprioritized reception in the time zone included in the second message,the communication station #3 is extracted.

The communication station #2 extracts only the records pertaining to thestations which the local station does not recognize (hidden terminals tothe local station or the next neighboring station) among the informationgroup stored in the second message, and makes a third message includingthe TBTT information of the extracted records. By indicating the TBTT bya relative time from the time of the ordinary beacon of thecommunication station #2, time can be informed even if the clockmanaging the whole system does not exist. Moreover, the communicationstation #2 transmits the made third message to the communication station#3. In the example shown in FIG. 18, the Ask as the third message istransmitted at a time T5.

The third message indicates that “there is the possibility that thecommunication station #2 collides with the reception of thecommunication station #1 in the transmission prioritized period TPP inthe TBTT included in the message”. In other words, the third messageindicates to the communication station #3 that there is the possibilitythat a signal addressed to the communication station #2 cannot always bereceived with priority in the TBTT.

Scanning and Change of TBTT

When the communication station #3, which has received the third message,recognizes that there is a problem with regard to the reception in thetransmission prioritized period TPP of the communication station #2, thecommunication station #3 activates the change processing of the TBTT forchanging the transmission time in the TPP addressed to the communicationstation #2.

In the TBTT changing processing, the communication station #3 performsthe scanning processing for the super frame, and searches a vacant TBTTin the time zone which is not described in the third message. Then, thecommunication station #3 tries to change the time zone for performing atransmission having a high priority addressed to the communicationstation #2.

Moreover, at the same time when the communication station #3 determinesto perform the scanning processing, the communication station #3 informsthe periphery of a schedule of changing the TBTT of the local station inthe ALERT field of the transmission beacon.

Then, the communication station #3 activates the scanning processing asshown in FIG. 18. When the scanning processing has ended, thecommunication station #3 searches the vacant TBTT by the proceduredescribed above in the consideration of the time zone recorded in thethird message as an NG time zone (which respect will be describedlater), and replaces the TBTT of the beacon performing a transmission inthe NG time zone at the present time. In the example shown in FIG. 18,the TBTT of the communication station #3 is replaced with the time T6.

Transmission of Fourth Message

When sufficient vacant TBTTs exist, the communication station #3 returnsto a state in which the transmission prioritized period TPP can beeffectively used by the processing described above. However, in a caseof no sufficient vacant TBTT existing, there is a possibility that thecommunication station #3 cannot deal with the request of thecommunication station #2 sufficiently. In a case where the communicationstation #3 performs communication also to another station, thecommunication station #3 schedules the transmission control in orderthat transmissions may be performed to the communication stations otherthan the communication station #2 at the time reported as NG by thecommunication station #2. Alternatively, there is also a case where thetransmission of a sub beacon at the time is stopped.

With an object of informing the communication station #2 of such asituation, the communication station #3 reports the existence of theTBTTs which could not be changed to the communication station #2. It isdesirable to report that all of the TBTTs have been changed as therequest to the communication station #2 even in the case where thecommunication station #3 could deal with the request of thecommunication station #2. The communication station #3 transmits theinformation to the communication station #2 as the fourth message. Inthe fourth message, the NG time at which beacons have still beentransmitted, though which time has been reported as the NG time in thethird message, is clearly described. In the example shown in FIG. 18,Status as the fourth message is transmitted at the time T7.

Transmission of Fifth Message

The communication station #2, which has received the fourth message,grasps how much the communication station #3 has responded the request,and the communication station #2 preserves the time zone (TBTT) reportedas one in which communication station #3 could not respond the requestby the communication station #3 as an “unsolved time zone” to takenotice lest the communication station #2 should be initiated a searchprocedure on the basis of a phenomenon produced in the time zone.Furthermore, the communication station #2 transfers the “unsolved timezone” information to the communication station #1 as a fifth message forowning the “unsolved time zone” information commonly with thecommunication station #1, which is in the similar sate. In the exampleshown in FIG. 18, Status as the fifth message is transmitted at the timeT8.

Reception of Fifth Message

The communication station #1, which has received the fifth message,similarly to the communication station #2, preserves the reported timezone (TBTT) as the “unsolved time zone”, and takes notice lest thesearch procedure should be initiated owing to the phenomenon generatedin the time zone.

H-5. Search Processing of Vacant TBTT in Consideration of NG Time Zone

As described above, it is necessary for the communication station whichhas received the Ask as the third message to set the beacon transmissiontiming TBTT for acquiring a transmission prioritized period TPP inconsideration of the state of a reception station pertaining to thetransmission in the TPP of the local station. The search processing of avacant TBTT performed in this case is described in the following withreference to FIG. 19.

In FIG. 19, it is supposed that the communication station #0transmitting Beacon-0 receives the third message, and FIG. 19 shows anexample of a case where the communication station #0 performs the searchprocessing of a vacant TBTT.

The communication station #0 setting a TBTT also in consideration of thestate of the reception station performs the scanning processing of onesuper frame. Thereby, it is supposed that beacons are received from theneighboring communication stations #1 and #2. In a case where the NBOIsincluded in the beacons are “NBOI of Beacon-1” and “NBOI of Beacon-2”,respectively, in FIG. 19, an Rx NBOI Table is made up by shifting theNBOIs and performing an OR operation in accordance with a proceduresimilar to the case described with reference to FIG. 13. The Rx NBOITable becomes the shown “OR of NBOIs (Rx NBOI Table)”.

Moreover, the communication station #0 makes up an NG Table in which 1is set in bits corresponding to the recording times included in thethird message on the basis of the time zone information received as thethird message. Then, an OR operation of the Rx NBOI Table and the NGTable is performed to make up a final NBOI Table. This is equivalent tothe Final NBOI Table in FIG. 19.

Now, the communication station #0 transmits two beacons in a superframe, and ascertains the existence of a beacon transmitted in the timezone about which 1 is set in the NG Table. In the example shown in FIG.19, the timing on the leftmost side on the paper surface is equivalentto that beacon, and the communication station #0 determines to changethe beacon transmission time.

A new beacon transmission time is selected from time zones which are notmarked in the final NBOI Table made up in the way described above. Inthe example shown in FIG. 19, a state in which a novel TBTT is set atthe sixth timing from the left end is shown. The communication station#0 marks the final NBOI Table at the time, and changes the leftmost TBTTto the sixth TBTT from the left end.

Incidentally, in a case where there is a plurality of beacons performinga transmission in the time zone at which 1 is set in the NG Table, theprocessing described above is repeatedly performed until all of theTBTTs are changed or until the final NBOI Table is all marked. Therebythe communication station #0 tries re-setting of the TBTT as many timesas possible.

H-6. Supplementary

It is noted that it is necessary that the search procedure and the TBTTchanging procedure are activated only in the time zones in which theappearance of the beacons of neighboring stations does not greatlychange for an object of avoiding the confusion caused by the activationof the search procedure and the TBTT changing procedure at the time of achange of a network topology or at the time of being activatedunnecessarily.

To put it concretely, activation of the search procedure and decoding ofthe message are performed after ascertaining the continuation of thestate over several super frames in which state the existence of thereception of beacons from the neighboring stations and the existence ofTBTTs are not changed and further NBAI/NBOI, ALERT, TxNum, Sense Leveland the like informed in the beacons are not changed as a result ofscanning processing.

Moreover, in a case where the existence of periphery beacons is changedowing to a change of the network topology or the like, there is a casewhere the “unsolved time zone” is cleared.

H-7. State after Procedure Activation

By following the procedure described above, the beacons of each stationshown in FIG. 14 are finally located, for example, as shown in FIG. 20.As shown in the drawing, the coincidence of the communication station #3and the TBTTs which does not need the communication station #3 isevaded.

However, because the number of the beacons which the communicationstations existing in the system transmit exceeds 8 which is the numberof TBTTs capable of being defined in a super frame, not all of thebeacons can be assigned in different TBTTs. In the example shown in FIG.20, the communication station #3 and the beacon of the communicationstation #3 are still transmitted in the same TBTT at the time T5.

In such a case, when a communication station judges that thecommunication station cannot provide a desired bandwidth to anapplication, there is a case where the communication station reportsthat it is impossible to provide a bandwidth suitable for a request tothe application.

Moreover, in such a case, when the communication station judges that thecommunication station cannot provide a desired bandwidth to theapplication, there is a case where a procedure for reducing thetransmission and reception range of the communication station tosuppress the reception of interference or the like is activated. In theexample shown in FIG. 20, it is possible to reduce the problem bynarrowing the transmission and reception range of the communicationstation #1 to drive the communication station #2 out of the range.However, the changing method of the transmission and reception range ofa communication station is not related to the subject matter of thepresent invention directly, and accordingly the further description isnot given here.

I. Dealing with Problem (Second Solution)

In the previous item H, the procedure for settling a problem after thegeneration of the problem is described. But, in the present item, thecontents of processing of adding processing previously lest a problemshould be generated are described.

I-1. Frame Format

FIG. 21 shows an example of the configuration of a frame format used inthe present embodiment. The example shown in the drawing is differentfrom the related art frame format shown in FIG. 26 in that a priorityfield indicating whether the signal is transmitted by prioritizedcommunication or not is added. In the shown example, a case where thepriority field is formed in the PLCP header is exemplified. But, thesubject matter of the present invention is not limited to the example.For example, the priority field may be formed in a MAC header.

The communication station sets 1 in the priority field to a signaltransmitted in the transmission prioritized period TPP of the localstation, and set 0 in the priority field to a signal transmitted in theother periods. Moreover, in a frame transmitted owing to the receptionof a certain signal such as the CTS transmitted in response to the RTS,the DATA transmitted in response to the CTS, and the like, the priorityfield set in the signal received immediately before is copied into thepriority field of the frame to be transmitted. That is to say, the valueof the priority field at the point of time of beginning a certaintransmission transaction is succeeded until the end of the transmissiontransaction.

However, the priority field is not limited to the binary information of0 and 1, but there is a case where a plurality of steps of priority isshown. For example, in a case when 8 bytes is allotted as the priorityfield, 256 steps of the priority can be set. In this case, the 256 stepsof priority can be set according to the importance of the application ofa signal to be transmitted or received, the inequality of transmissionchances owing to the existing positions of communication stations, andthe like. That is to say, a high priority value is set to an applicationhaving a high priority, or a high priority value is set also in a casewhere a communication station hardly obtain any transmission chancesbecause of avoiding the collisions with the transmission signals ofperipheral communication stations.

As described above, because sub beacons are transmitted with an objectdifferent from that of normal beacons, the sub beacons do notnecessarily include the information of the beacons in a normalsituation, and it is sufficient that a fact that they are “packetsaccompanied by the priority different from that of the ordinary packets”is described. In the present embodiment, the sub beacons may be definedby the existence of the priority field and by the storage of a valueindicating the highness of the priority into the priority field.

Incidentally, the expression of “being transmitted in prioritizedcommunication” in this section is concretely based on an assumption of acase where a certain communication station performs a transmission inthe transmission prioritized period TPP of the local station. That is tosay, the communication station sets 1 in the priority field in a framewhich performs a prioritized transmission in the TPP (or which is tryingto perform the prioritized transmission in the TPP).

I-2. Mark Procedure of Transmission-Reception Dangerous Zone

A communication station operates while keeping the TDMA structure asshown in FIG. 3, and manages one super frame as a plurality of timeslots obtained by dividing the super frame by TBTTs.

The communication station receives a signal, and decodes the PLCP headerthereof to refer to the priority field thereof. Thereby, thecommunication station judges whether the packet has been transmittedwith a prioritized transmission right or not. Here, in a case where itbecomes clear that the packet has been transmitted in the prioritizedtransmission, the fact is recorded. Moreover, when the decoding of thepacket until the MAC header has ended, the transmission source stationand the reception destination station of the packet becomes clear. Thecommunication station refers to these pieces of information to ascertainthat the reception destination station of the packet is not the localstation and that the packet does not located in a “range in which thelocal station can receive” the packet. When the fact is ascertained, thecommunication station ascertains the priority field recorded in advance.Moreover, the communication station may sometimes ascertain the priorityfield after only ascertaining that the reception destination station ofthe packet is not the local station. Hereupon, in a case where itbecomes clear that the packet has been transmitted with the prioritizedright, the communication station marks the time slot corresponding tothe time, and preserves the information as a “transmission-receptiondangerous zone”.

FIG. 22 shows a processing procedure for making thetransmission-reception dangerous zone. In the drawing, a time T0 is aTBTT of the communication station #3, and the communication station #3obtains the transmission prioritized period TPP by a fixed proceduresuch as an sub beacon transmission. Consequently, values equal to ormore than 1 are set in the priority fields of signals to be transmittedfrom the communication station #3 after the obtainment of the TPP tillthe expiration of the TPP (for the convenience of the description, it issupposed that a value 1 is set in the following). Moreover, in responseto the transmission signal from the communication station #3, a value 1is also set in the priority fields of the signals transmitted from thecommunication station #2. Consequently, in FIG. 22, in the priorityfields of the signals with hatching, the value 1 is set.

It is supposed that the communication station #1 can receive the signalsfrom the communication station #2 but the signals from the communicationstation #3 exist at positions where the communication station 1 cannotreceive the signals. In this case, the communication station #1 marksthe CTS signal received from the communication station #2 in the TPP ofthe communication station #3 generating from the time T0, and preservesthe time slot of the time T0 as the “transmission-reception dangerouszone”.

Incidentally, 0 is set in the priority fields of signals transmittedafter the expiration of the TPP and signals transmitted in response tothe former signals. Consequently, because 0 is set in the priority fieldof the CTS signal transmitted from the communication station #2 in thenext time slot beginning from the time T1, the communication station #1does not judge the time slot as the “transmission-reception dangerouszone”.

I-3. Mark Processing Flow of Transmission-Reception Dangerous Zone

FIG. 23 shows the processing procedure for marking thetransmission-reception dangerous zone in the shape of a flowchart. Inthe shown processing procedure, the processing which is partiallydifferent from the above description is shown. But even if eitherprocessing is performed, the desired advantages of the present inventioncan be realized.

When a communication station receives a signal (step S21), thecommunication station judges whether the destination of the receivedsignal is the local station or not (step S22). Then, in a case where thereceived signal is addressed to the local station, the communicationstation does not perform the “mark processing of transmission-receptiondangerous zone”.

On the other hand, in a case where the received signal is addressed toanother station, the communication station judges whether thedestination of the received signal is an adjacent station of the localstation or not (step S23). In a case where the destination of thereceived signal is a neighboring station, the communication terminaldoes not perform the “mark processing of transmission-receptiondangerous zone”. The judgment is not performed sometimes. The reason isthat the mark of the transmission-reception dangerous zone should beperformed independent of being a neighboring station or not.

On the other hand, in a case where the received signal is not addressedto any neighboring stations (step S23), the communication stationfurther examines the priority of the received signal (step S24). Here,in a case where the priority of the received signal is judged to be low,the processing of marking the transmission-reception dangerous zone isnot performed. On the other hand, in a case where the priority of thereceived signal is judged to be high, the time zone corresponding to thepresent time is marked as the “transmission-reception dangerous zone”,and the NG Table preserving the “transmission-reception dangerous zone”information is updated (step S25).

Moreover, the communication station also monitors the lapse of time, andincludes a function of judging whether a unit time such as a gap ofsuper frames has lapsed or not. The communication station judges whetherthe unit time has lapsed or not by the monitoring (step S26). Then, in acase where it is recognized that the unit time equivalent to the superframe has lapsed, the communication station performs the updating suchas deleting a part of the history of the NG Table being the“transmission-reception dangerous zone” information preserved until now(step S27). Thereby, the processing of clearing the past“transmission-reception dangerous zone” is executed, and the keeping ofthe latest “transmission-reception dangerous zone” can be performed.

I-4. Prioritized Transmission Procedure Part 1

For example, the procedure of a case where the transmission ofprioritized traffic is performed by using a sub beacon jointly isdescribed in the following with reference to FIG. 24. However, in theexample shown in the drawing, similarly to the case shown in FIG. 16, itis supposed that only the mutually adjacent communication stations arelocated within an electric wave arriving range. In the shown example, acase where the communication station #0 performs the transmission of theprioritized traffic to the communication station #1 is supposed.

When the communication station #0 is given a transmission request ofprioritized traffic from an upper layer of the communication protocol,the communication station #0 transmits a message (the message shown asScan in the drawing) to the communication station #1 being thedestination of the traffic which message notifies of the intension ofrequesting a report of “transmission-reception dangerous zone” owing tothe intension of the transmission of prioritized traffic.

The communication station #1, which has received the message, performsthe scanning processing for one super frame, and performs the extractionof the “transmission-reception dangerous zone” in accordance with theprocedure described above. The communication station #1 sends back amessage (the message shown by Update in the drawing) reporting theresults of the scanning and the extraction to the communication station#0. Moreover, the communication station #0 itself performs the scanningprocessing for grasping the position of a vacant time zone for aprioritized traffic transmission using a sub beacon transmissionjointly.

The communication station #0 receives the Update message from thecommunication station #1 so that the communication station #0 can graspwhich time zone is the dangerous time zone for the communication station#1. By using the procedure described with reference to FIG. 19 jointlywhile avoiding the dangerous time zone, the communication station #0determines the transmission time of the sub beacon for accommodating thetraffic addressed to the communication station #1 therein, and begins totransmit the sub beacon.

On the other hand, the communication station #1 continues to perform thescanning processing after that. Thereby the communication station #1receives the sub beacon from the communication station #0 to grasp atwhich time zone the communication station #0 determined to transmit thesub beacon. Thereby, the communication station #1 preserves the timezone as the time zone to be used for future reception.

I-5. Prioritized Transmission Procedure Part 2

A communication station performs the scanning processing at a fixedtime. Then, the communication station sets the NBOI bit of atransmission beacon on the basis of the information obtained by thescanning (namely at which time zone the beacon has been received).Moreover, the communication station informs by the NBAI bit of whichtime zone the reception of the beacon has been performed in. IfNBAI/NBOI bits are set in accordance with the rule described already,the information shown in the following table is informed. TABLE 2 NBAINBOI SITUATION IN THE TIME ZONE 0 0 EXISTENCE OF BEACONS IS NOTASCERTAINED IN THE TIME ZONE 0 1 EXISTENCE OF BEACONS IS GASPED IN THETIME ZONE, BUT RECEPTION PROCESSING OF THE BEACON IS NOT PERFORMED INTHIS TIME ZONE 1 1 EXISTENCE OF BEACONS IS GRASPED IN THE TIME ZONE, ANDRECEPTION PROCESSING OF THE BEACON IS PERFORMED IN THIS TIME ZONE

At the time of setting the NBOI and the NBAI bit, also the notifying ofthe information of the “transmission-reception dangerous zone” isconsidered. The NBOI bit and the like are fields made up on the basis ofthe information obtained by the results of scanning, and the informationof the “transmission-reception dangerous zone” is also the informationobtained by the result of scanning. Consequently, the intermixing ofthese pieces of information is structurally easy. As a result, theNBAI/NBOI bits are set as follows. TABLE 3 NBAI NBOI SITUATION IN THETIME ZONE 0 0 EXISTENCE OF BEACON IS NOT ASCERTAINED IN THE TIME ZONE,AND THE TIME ZONE IS NOT “TRANSMISSION-RECEPTION DANGEROUS ZONE” 0 1EXISTENCE OF BEACON IS GRASPED IN THE TIME ZONE, BUT RECEPTIONPROCESSING OF THE BEACON IS NOT PERFORMED IN THE TIME ZONE 1 1 EXISTENCEOF BEACON IS GRASPED IN THE TIME ZONE, AND RECEPTION PROCESSING OF THEBEACON IS PERFORMED IN THE TIME ZONE 1 0 EXISTENCE OF BEACON IS NOTGRASPED IN THE TIME ZONE, BUT THE TIME ZONE IS “TRANSMISSION- RECEPTIONDANGEROUS ZONE”

For example, when the NBAI/NBOI bits are “00”, the existence of anybeacons is not ascertained in the time zone (slot), and consequently itcan be concluded that the time zone is not a transmission-receptiondangerous zone. Moreover, because the combination of the NBAI/NBOI bitsbeing “10” is one of the bit string being impossible in an ordinarybeacon receiving operation, the present embodiment uses the combinationfor clearly indicating that the time zone is a transmission-receptiondangerous zone.

That is to say, in a case where a communication station which hasreceived a beacon performs a frame transmission to the beacontransmission station, the communication station can know the time zonein which reception is not guaranteed on the basis of the combination ofthe NBAI and NBOI of the received beacon. A convenient slot in a superframe (i.e. a slot being not a transmission-reception dangerous zone)can be discriminated. In other words, by decoding the combination of theNBAI and the NBOI of a beacon received from the frame transmissionpartner station, the communication station can perform transmissionwhile avoiding the transmission-reception dangerous zone.

As described above, by introducing a structure in which communicationstations inform of their transmission-reception dangerous zones to oneanother, the situation in which communication cannot performed owing tothe circumstances of a reception station as being exemplified by thetimes T0 and T5 in FIG. 15 can be avoided.

In the above description, in a case of the location of the communicationstations as shown in FIG. 15, for example, the communication station #2and the communication station #3 severally perform prioritizedcommunication. Consequently, the communication station #1 located in theneighborhood of the communication station #3 is in the state in whichthe communication station #1 cannot perform any transmission. In thiscase, the communication station #0 cannot know the transmissionpropriety situation of the communication station #1 independent of beingprioritized communication or not. Consequently, the communicationstation #0 performs a transmission to the communication station #1 invain, though the communication station #1 is in the transmissionimpossible state. On the contrary, the present embodiment can avoid sucha situation. That is to say, the communication station #0 can know thetime zone in which reception is not guaranteed on the basis of acombination of NBAI and NBOI of the beacon received from thecommunication station #0.

It is noted that in a case where sub beacons exist but the destinationof the communication transmitted by using the transmission prioritizedperiods TPP obtained from the sub beacons is fixed to a specificcommunication station, the communication station marks the NBAI/NBOIbits of the time zone (slot) in which the sub beacon addressed toanother station is received as “10”, and informs the communicationpartner of the local station or the like of a fact that the slot is the“transmission-reception dangerous zone”.

In a case where the NBAI/NBOI bits are defined as shown in Table 3, onthe side of the beacon reception station, it is dangerous to use thetime zone (slot) in which 1 is described as the NBAI, even if 0 isdescribed as the NBOI. Accordingly, it is preferable to deal with aresult of an OR (logical sum) operation of the mutual corresponding bitsof the NBAI and the NBOI of the received beacons as the NBOI. That is tosay, when a communication station which has received a beacon extractsnovel beacon transmission timing, the communication station judges thatall of the slots in which the NBAI/NBOI bits of the received beacon isnot described as “00” severally have a description of 1 as the NBOI bit.After that, the communication station searches the vacant slot in thesuper frame by the procedures shown in FIGS. 13 and 19 (namely theprocedures of operating the OR of each NBOI after aligning the offsets).The reason of the search is that the procedures shown in FIGS. 13 and 19are not essentially performed according to 1/0 of the NBOI bit, and thatthe procedures should be performed according to whether a predeterminedtime zone is vacant or not.

Moreover, in a case where the NBAI/NBOI bits are defined as shown inTable 3, on the side of the beacon reception station, even if 1 isdescribed as the NBAI, as long as the time zone (slot) in which 0 isdescribed as the NBOI, a transmission can be judged to be possible.Accordingly, it is preferable to deal with a result of AND (logicalproduct) operations of mutually corresponding bits of the NBAI and NBOIof the received beacon as the NBAI. That is to say, the communicationstation which has received a beacon sets only the time zones (slots) inwhich the NBAI/NBOI bits are marked as “11” as thetransmission-disallowed period at the time of the setting of thetransmission-disallowed period described pertaining to the section F.The reason is that in the time zones in which NBAI/NBOI bits are set as“10”, though the NBAI bit is set to be 1, the transmission station ofthe beacon informs of the nonexistence of the signal which the localstation intends to receive in the time zone, in other words, thetransmission station simultaneously suggests that there is nopossibility of hindering the reception of the transmission station ofthe beacon. As described above, the setting of thetransmission-disallowed period is not essentially performed according tothe bit string of 1/0 of the NBAI bits, but the setting should beperformed according to whether the reception of the beacon transmissionstation is hindered or not.

To summarize the above, as to the NBAI/NBOI field, what meaning theupper one bit (NBAI) and the lower one bit (NBOI) in each slot have isnot important, but it is important to inform the situation of each timezone (slot) in the super frame separated by every TBTT in a bit map suchas the NBAI/NBOI of the peripheral communication stations.

In a case where a communication station B transmitting a sub beacon withan object of accommodating the prioritized traffic addressed to acertain specific communication station A extracts a sub beacontransmission time zone from the time zones in which at least theNBAI/NBOI bits of the beacons transmitted from the communication stationA are set “00” by referring to the NBAI/NBOI bits of the communicationstation A, the communication by means of the transmission prioritizedperiod TPP can be stably provided.

Moreover, a communication station can grasp the transmission-receptiondangerous zone of a beacon transmission station by referring to theNBAI/NBOI bits of the beacons received from neighboring stations, andthe communication station can know that the communication station is inthe transmission-disallowed state in the transmission-receptiondangerous time zone.

Because the possibility that no responses can be obtained even whentransmission to a communication station is performed is high even in acase of not performing any prioritized transmission in atransmission-reception dangerous zone of the communication station, italso becomes possible to refrain the transmission to the communicationstation. Thereby, ineffectual transmissions can be reduced. In thiscase, the processing of giving up the transmission to the communicationstation for a while when no responses can be obtained after transmittingRTS to the communication station several times may be used jointly.

I-6. Supplementary Part 1

Operation examples in the other aspects in a case where thetransmissions and the receptions of signals by the prioritizedtransmission procedure describe in the preceding section I-5 aredescribed with reference to FIGS. 35, 36, 37, 41 and 42. In thefollowing description, it is supposed that five communication stationsof STA1, STA2, STA3, STA4 and STA5 exist.

FIG. 35 schematically shows a supposed network topology. In the shownexample, the STAL is located at a position where the STAL cancommunicate only with the STA2, the STA2 is located at a position wherethe STA2 can communicate with the STAL and the STA3, the STA3 is locatedat a position where the STA3 can communicate with the STA2 and the STA4,the STA4 is located at a position where the STA4 can communicate withthe STA3 and the STA5, and the STA5 is located at a position where theSTA5 can communicate only with the STA4.

FIG. 36 shows an example of the configuration of a super frame in anetwork topology as shown in FIG. 35. In the shown example, the superframe is defined as the beacon transmission interval of thecommunication stations. One super frame is composed of 16 TBTTs (slots)of T0 to T15.

In the super frame, it is supposed that each of the communicationstations STAL to STA5 sets beacon transmission time zones andprioritized transmission time zones at the timing as shown in FIG. 36.That is to say, the STAL performs a beacon transmission at a time T0,the STA2 performs a beacon transmission at a time T8, the STA3 performsa beacon transmission at a time T3, the STA4 performs a beacontransmission at a time T8, and the STA5 performs a beacon transmissionat a time T5. Moreover, the STAL and the STA2 perform prioritizedcommunication with each other at times T4, T6 and T9 and T10, and theSTA4 and the STA5 perform prioritized communication with each other attimes T2, T9 and T10, and T13.

Here, an ordinary beacon transmission times do not generate anycollisions between each communication station. On the other hand, amongthe time zones in which of each of the communication stations STA1,STA2, STA4 and STA5 performs prioritized communication, the prioritizedcommunication are simultaneously performed at times T9 and T10, and theSTA3 can simultaneously receive the prioritized communication.Consequently, collisions are generated. However, because both of theprioritized transmissions performed here are communication havingnothing to do with the STA3, it is not necessary for STA3 to receive thecommunication.

Consequently, in this case, the STA3 has a possibility that the STA3performs duplicate reception of sub beacons in the time zones of thesame TBTT. However, the STA3 does not recognize that as a collision sothat the STA3 does not activate the procedure for changing TBTT owing tothe collisions of beacons. As a result, the time arrangement shown inFIG. 36 is not treated as one in which collisions are generated, andcommunication operations are continued.

On the other hand, in a case where each communication station transmitsa signal at the timing shown in FIG. 37 in the same network topology asshown in FIG. 35, the beacons of the STA2 and the STA4 are transmittedat the same time (time T8), and the STA3 receives the them in the sametime zone. In this case, the STA3 judges that collisions of beacons aregenerated, and the STA3 transmits a message requesting the change ofbeacon transmission times to the either communication station STA2 orSTA4. The communication station which has received the message performsscanning processing to find a vacant slot in the super frame similarlyto the initial operation described above. Then, the communicationstation sets a novel TBTT to grow out of the beacon collision state.

Next, a case where, for example, the STA4 and the STA5 moved and eachcommunication station is arranged as shown in FIG. 41 is considered. Inthe example shown in the drawing, the STA2 and the STA4, which have notbeen located in a mutual communication area until now, have moved in arange capable of directly communicating with each other. In this case,if it is supposed that each communication station sets beacontransmission time zones and prioritized transmission time zones at thesame timing as that shown in FIG. 36, the time zones at the times T9 andT10 being a part of the prioritized transmission time zones of the STA2and the STA4 coincide with each other owing to the movements ofcommunication stations (see FIG. 42). Consequently, the coincidence isrecognized as a collision between the STA2 and the STA4. In this case,either communication station of the STA2 or the STA4 performs thescanning processing similarly to the initial operation described above,and thereby detects a vacant slot in the super frame. Then thecommunication station sets a novel TBTT for a prioritized communicationtime zone, and thereby the communication stations grow out of thecollision state of the prioritized communication time zones.

I-7. Supplementary Part 2 In the section I, descriptions have been givenuntil now on the basis of the supposition that each communicationstation transmits a beacon in a vacant slot (TBTT) in a super frame.According to the basic beacon transmission procedure, only one beacon isallowed to be disposed in each slot constituting the super frame.

On the other hand, in the present item, a network operation implementedwithout obeying the basic beacon transmission procedure described aboveis described with reference to FIGS. 38 to 40. There is a case where acommunication station determined to perform communication only with acertain specific communication station in a network transmits a beaconat different timing exceptionally. In the shown example, the STA2determines that the STA2 performs communication only with the STA1.

FIG. 38 shows a situation in which the STAL and the STA2 performcommunication with each other by a prioritized transmission at the timesT4, T6 and T9 and T10 similarly to the situation shown in FIG. 37.However, because it is determined that the STA2 performs communicationonly with the STAL in the example shown in FIG. 38, no beacontransmission timing TBTT only for the local station is set in the superframe, and in place of it, the transmission of a beacon is performed inthe prioritized communication time zone at the time T9.

Moreover, in the example shown in FIG. 39, with the beacon transmissionby the STA1 at the time T0 as the start, prioritized communication isperformed between the STA1 and STA2 in a period from the time T0 to thetime T1. Because it is determined that the STA2 performs communicationonly with the STA1, no beacon transmission timing TBTT only for thelocal station is set in the super frame. In place of it, the STA2performs a beacon transmission in the midst of the prioritizedcommunication by using the same slot as that for the beacon transmissionof the STAL being the communication partner.

The beacon transmission procedure of the STA2 in the situation shown inFIGS. 38 and 39 is drawn in FIG. 40 in detail. In FIG. 40, the timezones T0 and T1 in which the STAL performs prioritized communicationwith the STA2 is shown in enlarged scales.

Because the STAL is in the communication state with the STA2, the STALtransmits a signal generated by multiplexing the RTS with an ordinarybeacon (normal beacon) or a sub beacon to the STA2 when the STA1 entersthe prioritized transmission time zone. In response to the transmittedsignal, the STA2 sends back a CTS, and at this timing the STA2multiplexes a beacon of the local station together with the CTS totransmit the multiplexed signal. The prioritized communication betweenthe STAL and the STA2 after that is continued according to the RTS/CTSprocedure similarly to the way described above.

The procedure of the transmission of the beacon transmitted by such away differs from the beacon transmission procedure described above inwhich the beacon is transmitted after setting an ordinary TBTT. That isto say, a communication station determined to perform communication onlywith a specific communication station transmits a beacon of the localstation by the use of a period in which the prioritized communicationwith the specific communication station is performed. In the presentspecification, a beacon transmitted by the communication station havingspecified a communication partner, by the use of a communicationoperation with the specified communication partner, without using anordinary beacon transmission procedure is defined as a “parasiticbeacon”. Moreover, the communication station specified as thecommunication partner is called as a “parasitic destination”. Theparasitic beacon is brought into existence between the communicationstations which are in the so-called master-slave relationship. In theexample shown in FIGS. 38 to 40, the STAL operating as a masterapparatus is a parasitic destination of the STA2 operating as a slaveapparatus.

The frame format configuration of an ordinary beacon (normal beacon) hasbeen already described with reference to FIG. 11. In a case of aparasitic beacon, for example, a frame is transmitted after describing afact that it is a parasitic beacon into the Type field, and describing avalue indicating how much the parasitic beacon is delayed to betransmitted into the Delay field on the basis of the TBTT of the STALbeing a parasitic destination.

Thereby, the communication station which has received the parasiticbeacon recognizes that the beacon received is an exceptional beacondifferent from ones transmitted every super frame, and detects the TBTTof the communication station being the parasitic destination of theparasitic beacon. Thereby the communication station can perform thesynchronization processing of the TBTT. Moreover, even in a case wherethe communication station which has received the parasitic beacon hasreceived parasitic beacon in the time zone of the TBTT same as that ofthe other ordinary beacons, the communication station does not regardsthe situation as a collision of beacons, and does not activate the TBTTchange procedure. It is needless to say that, even in a case where thecommunication station receives two or more parasitic beacons in a singletime zone of the TBTT, the communication station does not regard thesituation as the collision of beacons and does not activate the TBTTchange procedure.

I-8. Supplementary Part 3

In this item, the contents of processing in the situation described withregard to the supplementary part 1 is described more minutely withreference to FIGS. 43 to 45.

FIG. 43 shows an example of the arrangement of communication stationssupposed in the following description. In the shown example, there arefive communication stations from STA1 to STA5. Then, the STA1, the STA2and the STA3 are located at positions within a range in which thecommunication stations can mutually communicate, and the STA4 and theSTA3 are located at positions within a range in which the communicationstations can mutually communicate. Furthermore the STA4 and the STA5 arelocated within a range in which the communication stations can mutuallycommunicate. In a case where such an arrival range of a signal is given,the behavior of the STA3 according to each situation is described withreference to FIGS. 44 and 45. Incidentally, the abscissa axes shown inFIGS. 44 and 45 indicate time, and an interval from the time T0 to thetime T1 indicates a slot, namely the interval of the beacon transmissiontiming TBTT.

In the example shown in FIG. 44, the STA1 transmits an ordinary beacon(G-Bcn) at the time T0. Then, the STA2 specifies only the STAL as acommunication partner, and the STA2 uses the same time zone T0 totransmit a parasitic beacon (A-Bcn).

In this case, the STA3 receives the beacons of both of the STAL and theSTA2 in the same time zone T0. Because one of the received beacons induplication is a parasitic beacon, the STA3 does not recognize thebeacons as a collision of the beacon transmission timing TBTT, and doesnot activate the TBTT change procedure. Moreover, at the bit positionsequivalent to the time zone T0 of the NBAI/NBOI recorded in a beacontransmitted by the STA3, “11” (indicating the existence of a beacon atthat time and the desire of unhindered reception) is set in a case wherethe STA3 receives a beacon of the STA1, or “01” (indicating theexistence of a beacon at the time and a not received state) is set in acase where the STA3 does not receive any beacons from the STAL.

Moreover, in FIG. 44, in each time zone of the times T2, T3 and T4,prioritized communication is performed between the STA1 and the STA2.These signals are also received by the STA3 although they are notnecessary to be received by the STA3. Moreover, at the times T3 and T4,the prioritized communication is performed between the STA4 and theSTA5. These signals are also received by the STA3 although they are notnecessary to be received by the STA3.

In such a situation, the collision of signals is generated in the STA3,but there are no communication stations which are troubled by thecollision. Consequently, the STA3 does not recognize the collision asthe collision in the prioritized transmission time zone, and does notactivate the TBTT change procedure. Moreover, at a bit positionequivalent to the time zone of the NBAI/NBOI of a beacon transmitted bythe STA3, “10” (indicating the existence of a signal having nothing todo with the local station and being the “transmission-receptiondangerous zone”) is set.

A neighboring station which has received a beacon from the STA3 refersto a bit string of the NBAI/NBOI, and finds the “10” set in theNBAI/NBOI bit at the bit position corresponding to the T3 and T4 of thesuper frame. Thereby, the neighboring station recognizes that these timezones are the transmission-reception dangerous zones for the STA3.Because there is a high possibility of returning no replies even iftransmission to the STA3 is performed in the transmission-receptiondangerous zones, the neighboring station can also restrain thetransmission to the STA3.

Moreover, in FIG. 44, in the time zone of the time T6, the STAL and theSTA4 transmit an ordinary beacon (G-Bcn) in the same time zone. When thetransmission times of both beacons shift from each other owing to theshifts of TBTT offset in each beacon transmission station, the STA3 canrecognize that these duplicate beacons are transmitted in the same timezone.

In this case, the STA3 activates the TBTT change procedure, andtransmits a message to either communication stations of the STAL or theSTA4 for informing the communication station of the desire of changingthe TBTT. Moreover, at the bit position equivalent to the time zone ofthe NBAI/NBOI of the beacon transmitted by the STA3, “11” (indicatingthe existence of a beacon at the time and the desire of not beinghindered) is set in a case where the STA3 receives the beacon of theSTA1, or “01” (indicating the existence of a beacon at the time and thestate of being not received) is set in a case where the STA3 does notreceive any beacons of the STAL.

Moreover, FIG. 45 shows the situations judged to be a collision ofsignals by the STA3 at each time zone T0, T2, T4 and T6.

In the time zones shown at the times T0 and T2 in FIG. 45, STA1transmits an auxiliary beacon (S-Bcn), and the prioritized communicationis performed between the STA1 and the STA2. These signals are alsoreceived by the STA3 although they are not necessary to be received bythe STA3. Moreover, an ordinary beacon (G-Bcn) of the STA4 istransmitted in the same time zone. When the transmission times of bothbeacons shift from each other owing to the shifts of TBTT offset in eachcommunication station, the STA3 recognizes that these duplicate beaconsare transmitted in the same time zone. In this case, the STA3 activatesthe TBTT change procedure to transmit a message informing any one of thecommunication stations STA1, STA2 and STA4 of a desire of changing theTBTT.

Incidentally, here, a case where the STA1 and the STA3 are beyond thelimits of communication is supposed. At the time T2, the STA3 cannotreceive the sub beacons of the STA1, but can judge that prioritizedcommunication is performed in the time zone in the neighborhood byreferring to the priority field of the signal from the STA2.Accordingly, the STA3 transmits a message informing either communicationstations of the STA2 and the STA4 of the desire of changing its TBTT.

Also, in FIG. 45, in the time zone of the time T4, the STA3 transmits asub beacon (S-Bcn), and the prioritized communication is performedbetween the STA3 and the STA2. Moreover, in the same time zone, a normalbeacon (G-Bcn) of the STA4 is transmitted. Then, when the transmissiontimes of the mutual beacon signals shift from each other owing to theshift of the TBTT offset, the STA3 or the STA4 recognizes that theytransmit signals in the same time zone.

In this case, the STA3 or the STA4 judges that the TBTT which the localstation uses collides, and either station activates the TBTT changeprocedure to grow out of the collision state.

Moreover, in FIG. 45, in the time zone of the time T6, the prioritizedcommunication is performed between the STA3 and the STA2. Moreover, inthe same time zone, the prioritized communication is performed betweenthe STA4 and the STA5. Then, when the transmission times of the mutualsignals shift from each other owing to the shift of the TBTT offset, theSTA3 or the STA4 recognizes that they transmits signals in the same timezone.

In this case, the STA3 or the STA4 judges that the TBTT which the localstation uses collides, and either station activates the TBTT changeprocedure to grow out of the collision state.

In the above, the specific embodiments are referred to while the presentinvention is described in detail. However, it is apparent that a personskilled in the art can modify and substitute the embodiments withoutdeparting from the scope and the sprit of the present invention.

Although in the present specification, descriptions have been given to afollowing principal embodiment, but the subject matter of the presentinvention is not limited to the principal embodiment. The principalembodiment concerns the case where, in a self-organized distributiontype wireless network, when each communication station evades collisionsaccording to the detection of transmission signals from the othercommunication station while performing access control to a medium, eachcommunication station sets a range within which the local station canperform communication.

The present invention can publicly applied to a communication system aslong as each communication station secures a band in which the stationcan perform transmission with priority to perform a data transmissionsuch as a communication system for performing medium access controlrandomly according to occupying state of the medium like a CSMA, or acommunication system for performing medium access control by TDMA.

Moreover, in the present specification, descriptions have been chieflygiven to embodiment in which the present invention is applied to aself-organized distribution type wireless network, but it is needless tosay that the present invention can be similarly applied to networkshaving the formats other than the self-organized distribution type.

Moreover, the present invention can be applied to the medium accesscontrol in each channel of a multi-channel type communication system inwhich each communication station perform hopping over a plurality offrequency channels while performing communication.

Moreover, in the present specification, though a wireless LAN has beenexemplified for describing the embodiments of the present invention, thesubject matter of the present invention is not limited to the wirelessLAN. The present invention can be suitably applied to a communicationsystem such as an Ultra Wide Band performing signal transmission andreception in a lower SNR environment.

In short, the present invention has been disclosed in the form ofexemplification, and accordingly the contents described in the presentspecification should not be interpreted limitedly. For judging thesubject matter of the present invention, the claims described at thehead of the specification should be considered.

1. A wireless communication system in which each communication stationsets a prioritized utilization region of a local station to performframe transmission with priority, wherein: each communication stationcancels a transmission-disallowed state and sends back a frameresponding to a prioritized transmission frame addressed to the localstation in response to reception of the prioritized transmission framein a prioritized utilization region of a neighboring station during aperiod of waiting a transmission on the basis of detection of a signal.2. The wireless communication system as claimed in claim 1, wherein: ina case where the communication station cancels thetransmission-disallowed state, the communication station judges thatthere is a possibility that some problem is generated in the prioritizedutilization region, and determines to begin a search procedure so as tocarry out a processing evading duplication of transmission prioritizedperiods through the search procedure.
 3. A wireless communication systemin which each communication station sets a prioritized utilizationregion of a local station to perform frame transmission with priority,wherein, in a case where a second communication station recognizes thata signal from a third communication station is received in a time zonein which a transmission using a prioritized utilization region isperformed from a first communication station to the second communicationstation: said second communication station determines to begin thesearch procedure, and transmits a first message requiring said thirdcommunication station to report its reception state, said thirdcommunication station sends back a second message including theinformation pertaining to the communication stations being intransmission-reception states using the prioritized utilization regionin response to said first message, said second communication stationtransmits a third message to the first communication station which thirdmessage requests evasion of the transmission in the time zone which isdescribed in said second message and in which said third communicationstation performs transmission and reception using the prioritizedutilization region, and said first communication station changes thetransmission time zone addressed to the second communication station inresponse to the third message.
 4. The wireless communication system asclaimed in claim 3, wherein: said second communication station extractsonly entries of the communication stations which are not recognized bythe local station on the basis of said second message and transmits thethird message to said first communication station which the thirdmessage requests restraint of transmissions in the time zones includedin the extracted entries.
 5. The wireless communication system asclaimed in claim 3, wherein: said first communication station changesthe transmission time zone addressed to the second communication stationafter ascertaining a vacant state of media through signal detection. 6.The wireless communication system as claimed in claim 3, wherein: saidfirst communication station sends back a fourth message to the secondcommunication station which fourth message reports a result of thechange with regard to whether the first communication station couldsatisfy the request recorded in the third message or not after changingthe transmission time zone in response to said third message, and saidsecond communication station judges propriety of generation of a futurenew first message on the basis of contents of said fourth message. 7.The wireless communication system as claimed in claim 6, wherein: saidsecond communication station transfers said fourth message to said thirdcommunication station in a case where said second communication stationcould not satisfy the request described in said third message, and saidthird communication station judges propriety of generation of a futurenew first message on the basis of the contents of said fourth message.8. The wireless communication system as claimed in claim 3, wherein:said first communication station stops the transmission operation atleast in a part of the prioritized utilization region for said secondcommunication station in a case where said first communication stationcannot satisfy the request described in said third message from saidsecond communication station.
 9. The wireless communication system asclaimed in claim 3, wherein: said first communication station utilizesat least a part of the prioritized utilization region for said secondcommunication station in a transmission operation addressed to a stationother than said second communication station in a case where said firstcommunication station cannot satisfy the request described in said thirdmessage from said second communication station.
 10. A wirelesscommunication system in which each communication station sets aprioritized utilization region of a local station to perform frametransmission with priority, wherein, in a case where a secondcommunication station recognizes that a signal from a thirdcommunication station is received in a time zone in which a transmissionusing a prioritized utilization region is performed from a firstcommunication station to the second communication station: said secondcommunication station transmits a second message including informationpertaining to communication stations in a transmission-reception stateto said third communication station using the prioritized utilizationregion, said third communication station transmits a third messagerequesting evasion of transmission in a time zone which is described insaid second message and in which the second communication stationperforms transmission and reception using the prioritized utilizationregion to a fourth communication station to be a communication partnerof the local station, and said fourth communication station changes atransmission time zone addressed to said third communication station inresponse to said third message.
 11. A wireless communication system inwhich each communication station sets a prioritized utilization regionof a local station to perform frame transmission with priority, wherein:a communication station which received a frame containing informationindicating priority of the frame transcribes priority information onto aframe to be transmitted in response to the frame reception to performtransmission.
 12. The wireless communication system as claimed in claim11, wherein: said frame to be transmitted in response to the framereception is a control frame.
 13. The wireless communication system inwhich each communication station sets a prioritized utilization regionof a local station to perform frame transmission with priority, wherein:each communication station preserves, in response to reception of aprioritized transmission frame not addressed to the local station, areception time zone of the frame as a transmission-reception dangerouszone.
 14. The wireless communication system as claimed in claim 13,wherein: a communication station performing the prioritized transmissiontransmits to a partner station of the prioritized transmission a messagerequesting reporting of the transmission-reception dangerous zone; thepartner station sends back a response message reporting thetransmission-reception dangerous zone that a local station preserves,the communication station performing the prioritized transmission sets aprioritized transmission utilization region in a time zone other thanthe transmission-reception dangerous zone on the basis of a descriptionin the response message to perform the prioritized transmission andnotifies information regarding to the transmission-reception dangerouszone, and in a case receiving a notification signal regarding thetransmission-reception dangerous zone from a neighboring station, thecommunication station transmits a frame addressed to a communicationstation other than the neighboring station.
 15. The wirelesscommunication system as claimed in claim 13, wherein: a communicationstation performing the prioritized transmission transmits to a partnerstation of the prioritized transmission a message requesting reportingof the transmission-reception dangerous zone; the partner station sendsback a response message reporting the transmission-reception dangerouszone that a local station preserves, the communication stationperforming the prioritized transmission sets a prioritized transmissionutilization region in a time zone other than the transmission-receptiondangerous zone on the basis of a description in the response message toperform the prioritized transmission and notifies information regardingto the transmission-reception dangerous zone, and in a case receiving anotification signal regarding the transmission-reception dangerous zonefrom a neighboring station, the communication station sets a prioritizedutilization region for a communication station other than theneighboring station.
 16. A wireless communication system in which eachcommunication station sets a prioritized utilization region of a localstation to perform frame transmission with priority, wherein: acommunication station communicating only with a specific communicationstation transmits a beacon signal describing a communication state ofthe local station by using the prioritized utilization region with saidspecific communication station.
 17. The wireless communication system asclaimed in claim 16, wherein: a communication station not limiting acommunication partner transmits a normal beacon signal describing thecommunication state of the local station every predetermined frameperiod, and said communication station communicating only with saidspecific communication station transmits the beacon signal using abeacon transmission procedure of said specific communication station.18. The wireless communication system as claimed in claim 17, wherein:said frame period includes a plurality of beacon transmission timing,communication stations each not limiting a communication partner are notallowed to mutually transmit the ordinary beacon signal at a same beacontransmission timing, and said communication station communicating onlywith said specific communication station is allowed to transmit thebeacon signal at a same beacon transmission timing as that of saidspecific communication station.
 19. The wireless communication system asclaimed in claim 18, wherein: said communication station communicatingonly with said specific communication station describes in the beaconsignal that the beacon signal is a parasitic beacon to be transmittedusing the beacon transmission procedure of said specific communicationstation, and a communication station receiving the parasitic beacon doesnot judge that the parasitic beacon indicates a collision of beaconseven if said communication station receives the parasitic beacon at asame beacon transmission timing as that of said specific communicationstation.
 20. A wireless communication system establishing a network bytransmitting/receiving a beacon signal, wherein: a communication stationtransmitting the beacon signal describes discrepancy information of atransmission time in the beacon signal, in a case where the beaconsignal is transmitted at a different time from a scheduled time due toan unexpected happening.
 21. A wireless communication apparatus settinga prioritized utilization region to perform frame transmission withpriority, said apparatus comprising: communication means fortransmitting and receiving wireless data on a channel; media monitoringmeans for monitoring a occupation state of media; and communicationcontrol means for controlling a communication operation by saidcommunication means on the basis of the occupation state of the mediaascertained by said media monitoring means, wherein: said communicationcontrol means cancels a transmission-disallowed state and sends back aframe responding to a prioritized transmission frame in response to areception of the prioritized transmission frame addressed to a localstation in a prioritized utilization region of a neighboring stationduring a period of transmission waiting based on a signal detection. 22.A wireless communication apparatus as claimed in claim 21, wherein: saidcommunication control means judges that there is a possibility that someproblem occurs in the prioritized utilization region in a case ofcanceling the transmission-disallowed state to determine to begin asearch procedure for trying to find a cause, and executes processing forevading duplication of a transmission prioritized period through thesearch procedure.
 23. A wireless communication apparatus for setting aprioritized utilization region to perform frame transmission withpriority, said apparatus comprising: communication means fortransmitting and receiving wireless data on a channel; and communicationcontrol means for controlling a communication operation using theprioritized utilization region, wherein: said communication controlmeans determines to begin a search procedure and executes processing forevading duplication of the prioritized utilization region on the basisof a result of the search procedure in response to receiving aprioritized transmission frame not addressed to a local station fromanother communication station in a time zone in which said othercommunication station performs a transmission addressed to the localstation by the use of the prioritized utilization region.
 24. Thewireless communication apparatus as claimed in claim 23, wherein: saidcommunication control means transmits a first message requestingreporting of a reception situation to said other communication stationbeing a source of the prioritized transmission frame not addressed tothe local station, and transmits a third message requesting evadingtransmission in a time zone in which prioritized utilization regionsduplicate to a communication station performing a transmission to thelocal station using the prioritized utilization region on the basis of adescription of a second message being a response to said first message.25. The wireless communication apparatus as claimed in claim 23,wherein: said communication control means transmits a second messagerequesting reporting of a reception situation of the local station tosaid other communication station being a source of the prioritizedtransmission frame not addressed to the local station.
 26. The wirelesscommunication apparatus as claimed in claim 24 or 25, wherein: saidcommunication control means extracts only an entry of a communicationstation which the local station does not recognize from said secondmessage in response to receiving said second message, and transmits saidthird message requesting restraint of transmission in a time zoneincluded in the extracted entry to a communication station performingtransmission to the local station using the prioritized utilizationregion.
 27. The wireless communication apparatus as claimed in claim 24,wherein: said communication control means changes a transmission timezone after ascertaining a vacant state of a medium by a signal detectionin response to receiving said third message.
 28. The wirelesscommunication apparatus as claimed in claim 24, wherein: saidcommunication control means sends back a fourth message reportingwhether said apparatus can satisfy a request described in said thirdmessage or not after changing the transmission time zone in response tosaid third message.
 29. The wireless communication apparatus as claimedin claim 24, wherein: said communication control means stops atransmission operation at least a part of the prioritized utilizationregion in a case where said apparatus cannot satisfy a request describedin said third message.
 30. The wireless communication apparatus asclaimed in claim 24, wherein: said communication control means utilizesat least a part of the prioritized utilization region for a transmissionoperation addressed to another communication station in a case wheresaid apparatus cannot satisfy a request described in said third message.31. A wireless communication apparatus for setting a prioritizedutilization region to perform frame transmission with priority, saidapparatus comprising: communication means for transmitting and receivingwireless data on a channel; a receive data analyzing unit for extractingpriority information containing whether or not a reception frame istransmitted in the prioritized utilization region; and a transmissiondata generating unit for setting priority information of a transmissionframe, wherein: the priority information extracted by said receive dataanalyzing unit is transcribed in the transmission frame prior totransmitting a signal in response to the reception frame.
 32. Thewireless communication apparatus as claimed in claim 31, wherein: theframe to be transmitted by sad transmission data generating unit inresponse to the reception frame is a control frame.
 33. A wirelesscommunication apparatus for setting a prioritized utilization region toperform frame transmission with priority, said apparatus comprising:communication means for transmitting and receiving wireless data on achannel; and communication control means for controlling a communicationoperation using the prioritized utilization region, wherein: saidcommunication control means preserves a received time zone of aprioritized transmission frame not addressed to a local station as atransmission-reception dangerous zone in reception to receiving theframe.
 34. The wireless communication apparatus as claimed in claim 33,wherein: said communication control means transmits a message requestingreporting of the transmission-reception dangerous zone to a partnerstation of prioritized transmission at the time of performing theprioritized transmission.
 35. The wireless communication apparatus asclaimed in claim 34, wherein: said communication control means performsthe prioritized transmission by setting a prioritized transmissionutilization region in a time zone other than the transmission-receptiondangerous zone preserved by the partner station of the prioritizedtransmission.
 36. The wireless communication apparatus as claimed inclaim 33, said apparatus further comprising: transmission-receptiondangerous zone informing means for informing a neighboring station ofinformation pertaining to the transmission-reception dangerous zone. 37.The wireless communication apparatus as claimed in claim 36, whereinsaid communication control means performs the frame transmission inorder to avoid the transmission-reception dangerous zone described in anotification signal received from a transmission destination of theframe in a case of performing transmission addressed to a transmissiondestination communication station of the frame.
 38. The wirelesscommunication apparatus as claimed in claim 36, wherein: saidcommunication control means performs transmission addressed to acommunication station other than a transmission destination of the framein the transmission-reception dangerous zone described in a notificationsignal received from the transmission destination of the frame.
 39. Thewireless communication apparatus as claimed in claim 36, wherein saidcommunication control means sets a prioritized utilization region for acommunication station other than a transmission destination of theframe.
 40. A wireless communication system establishing a network bytransmitting/receiving a beacon signal, said wireless communicationsystem comprising: communication means for transmitting and receivingwireless data on a channel; communication control means for controllinga time for transmitting/receiving the beacon signal; and a transmissiondata generating unit for setting information to be described in atransmission beacon signal, wherein: said communication control meanssets a scheduled beacon transmission time, and changes the transmissiontime of the beacon signal in accordance with a used state of thechannel, and said transmission data generating unit describesdiscrepancy information between the scheduled beacon signal transmissiontime and an actual transmission time in the beacon signal.
 41. Awireless communication system establishing a network bytransmitting/receiving a beacon signal, said wireless communicationsystem comprising: communication means for transmitting and receivingwireless data on a channel; communication control means for controllinga time for transmitting/receiving the beacon signal; and a receive dataanalyzing unit for extracting discrepancy information between areception time of the beacon signal and a transmission time obtainedfrom a reception beacon signal, wherein: said communication controlmeans sets a scheduled beacon reception time, and said receive dataanalyzing unit extracts a scheduled transmission time of the beaconsignal from the discrepancy information between the reception time ofthe beacon signal and the transmission time described in the beaconsignal.
 42. A wireless communication method for setting a prioritizedutilization region to perform frame transmission with priority, saidmethod comprising the steps of: waiting a transmission on the basis of asignal detection; removing a transmission-disallowed state to send backa frame responding to a prioritized transmission frame addressed to alocal station in response to receiving the prioritized transmissionframe in a prioritized utilization region of a neighboring stationduring a period of waiting the transmission; judging that there is apossibility that some problem occurs in the prioritized utilizationregion in a case of canceling the transmission-disallowed state todetermine to begin a search procedure for trying to find a cause; andexecuting processing for evading duplication of transmission prioritizedperiods through the search procedure.
 43. A computer program describedin a computer readable format for executing the processing to set aprioritized utilization region for performing frame transmission withpriority on a computer system, the program including: a step of waitinga transmission on the basis of signal detection, a step of canceling atransmission-disallowed state and sending back a frame responding to aprioritized transmission frame addressed to a local station in answer toreception of the prioritized transmission frame in a prioritizedutilization region of a neighboring station during a period of waiting atransmission, a step of judging that there is a possibility that someproblem is generated in the prioritized utilization region in a casewhere the transmission-disallowed state is cancelled, and of determiningto begin a search procedure for trying to find a cause, and a step ofexecuting processing of evading duplication of transmission prioritizedperiods through the search procedure.